Dodwell: The Obliquity of the Ecliptic





The great Stone Circle of Stonehenge, on Salisbury Plain, Wiltshire, England, is one of the most famous monuments of ancient times in Britain. 


The astronomy of Stonehenge is of special interest, owing to the manner in which the axis of the monument is directed towards the point of sunrise on the North-Eastern horizon, at the date of the summer solstice, June 21, in each year.  If, therefore, the bearing or azimuth (the angle East from North) of the axis is measured, then the corresponding declination of the sun (i.e. its distance from the celestial equator in the heavens), or what amounts to the same thing, the Obliquity of the Ecliptic, can be calculated.  From this, we should be able, by the use of Newcomb’s Formula, to find very closely the date when the axis of Stonehenge was established, i.e. the date of construction of the Stonehenge monument, provided that Newcomb’s Formula gives the true place of the Sun in ancient times.

But, just as the foregoing study of the Great Solar Temple of Amen Ra at Karnak has shown that Newcomb’s Formula, by itself, gives a date so far remote as to be quite out of the question, so we shall see in this study of Stonehenge that the Formula similarly gives a date for its construction more than a thousand years earlier than the probable true date, based upon the most modern and thorough archaeological investigations.  Moreover, it will be seen that in both cases, when Newcomb’s Formula is corrected for the effects of the movement of recovery of the earth’s axis from its earlier disturbance, we then obtain dates for both Karnak and Stonehenge in agreement alike with history and archaeology.

The astronomical aspect of Stonehenge has always been of widespread public interest in Britain, and to this day crowds of people make a pilgrimage every year to the monument, and spend the night in considerable discomfort in order to watch the sun rise over the “Friar’s Heel Stone” on Mid-summer Day, and to witness the ceremonies of the modern Order of Druids.  This orientation to the Mid-summer sunrise point was clearly carried out by the designer or designers of Stonehenge with great care, as will be seen in the course of this study.  It is in keeping with the remarkable architecture of the principal portion of the Monument, which is much in advance of the more primitive structures in Britain, and suggests a later date than these.

Sir Norman Lockyer, who was one of the greatest British astronomers of his time, published a most interesting book in 1906, entitled Stonehenge and Other British Stone Monuments Astronomically Considered.”  He had previously carried out extensive examinations of Greek and Egyptian temples oriented to the Sun and, in some cases, apparently to certain bright stars.  His work on the Great Solar Temple of Amen Ra at Karnak, referred to in the previous chapter, is specially memorable.

In the year 1901 he made similar astronomical observations at Stonehenge, and examined with great care this and other ancient British Stone monuments which have an astronomical character.  The alignment of the axis of Stonehenge to the midsummer sunrise point, as shown by Sir Norman Lockyer, coincided not only with the central line of the “Avenue” (which will be described later), but also with the line joining two  distant sighting marks on the horizon, at opposite extremities of the axis line.

The first, in the exact prolongation of the central line of the Avenue towards the midsummer sunrise point, was an ancient British fortification situated on the summit of Sidbury Hill, 8 miles distant from Stonehenge to the North-East.  The second, towards the South-West, or midwinter sunset point, and equally in line with the axis of the monument, produced in that direction, was marked by the Grovely fortification, at a distance of 6 miles from Stonehenge.  Both these fortifications are prehistoric, and are believed by archaeological authorities to be of Early Iron Age.  This opinion was expressed by Mr. O.G.S. Crawford, Archaeology Officer of the British Ordnance Survey, who surveyed Stonehenge from the air (see “Article on Stonehenge and Karnak,” by A.R. Hinks, in XIX Century Magazine, July, 1925, p. 127).   We shall see, later on, the bearing of this matter on the date of construction of Stonehenge.

The care taken with the orientation of Stonehenge, and the manner in which it was linked with these distant sighting marks on the horizon, both to the midsummer sunrise point in the North-East and to the midwinter sunset point in the South-West, suggests that this central line indicates the solstitial position of the sun, both at midsummer and at midwinter, at the date of the foundation of the monument.  The astronomical date, derived from a true curve of the Obliquity of the Ecliptic for ancient times, should therefore agree with the date of the monument found by Archaeology, if the latter is also correctly established.

Now, it is of great interest to note that Sir Norman Lockyer, from his careful astronomical observations in 1901, found that the mean azimuth of the axis line of Stonehenge, as well as he could determine it, was 49° 35’ 51” East of  North.  These observations were made by Sir Norman in conjunction with Mr. F.C. Penrose, an eminent archaeologist and astronomer, who had previously made a notable study of the astronomical orientation of ancient Greek temples.

He then says that this result “is confirmed by the information also supplied from the Ordnance Survey, that from the centre of the Temple, the bearing to the North-East of the principle bench mark on a hill, about 8 miles distant, the bench mark being very near a well known ancient fortified British encampment named Silbury or Sidbury, is 49° 34’ 18”; and that the same line continued through Stonehenge, to the south-west, strikes another ancient fortification, namely Grovely Castle, about 6 miles distant.  For the above reasons 49° 34’ 18” has been adopted for the azimuth of the Avenue.”

Sir Norman then goes on to determine “what value should be given to the Sun’s declination when it appeared showing itself 2’ above the horizon, the azimuth being 49° 34’ 18”.”  This estimation of 2’ (or about 1/15 of the sun’s diameter) as marking the point of visible sunrise is a reasonable one, as most people noting the phenomenon of sunrise would probably agree.

The latitude of Stonehenge is 51° 10’ 42” N.;  and with this and the other necessary data, Sir Norman Lockyer calculated  “The Sun’s declination works out at 23° 54’ 30” N., and by Stockwell’s tables of the Obliquity, which are based upon determinations of the elements of the solar system, the date is found to be 1680 B.C.”  Sir Norman then goes on to say that “on account of the slight uncertainty as to the original line of observation, and the very slow rate of change in the obliquity of the Ecliptic, the date thus derived by be in error by 200 years more or less; this gives us a date of construction lying between, say, 1900 and 1500 B.C.”  He therefore adopted the mean date of 1700 B.C. as the probable date of the foundation of Stonehenge.

He then points out that “an independent archaeological enquiry carried out, in a most complete and admirable way, just after Mr. Penrose and myself had obtained our conclusion, entirely corroborates the date at which we had arrived.”  This archaeological enquiry was carried out in the summer of the same year, 1901, by Professor Gowland, the archaeologist, who was commissioned to conduct and examine archaeologically the excavations necessary in connection with the re-erection of the celebrated “leaning stone,” which was the Western upright of the great Central Trilithon.

The Eastern upright was still lying on the ground, broken into two pieces, up to the middle of 1958, when it was re-erected.  But at the date when it fell the companion western upright was left standing, but in a leaning position.  A fracture had developed in it, and the angle of leaning had increased so that it was feared that it, too, would fall.  Consequently, its re-erection was “recommended to Sir Edmund Antrobus (the owner of Stonehenge) by the Society of Antiquaries of London, and other learned bodies, and this re-erection was conducted at his desire and expense.” (see Sir N. Lockyer, Stonehenge, 1909 Edition, p. 69.)

Professor Gowland thoroughly studied the large number of archaeological specimens which he found, viz., flint instruments, consisting of stone axes, hammer-stones, hammer-axes, mauls weighing from 40 to 64 pounds, also large quantities of chippings of Sarsen and blue stones.  He came to the conclusion, on these and other grounds, that Stonehenge was built about the end of the Neolithic, or beginning of the Bronze Age in Britain and he finally stated

In my opinion, the date when copper or bronze was first known in Britain is a very remote one…the beginning of their application to practical uses should, I think, be placed at least as far back as 1800 B.C., and that date I am inclined to give, until further evidence is forthcoming, as the approximate date of the erection of Stonehenge.

It may be mentioned here that Newcomb’s Formula for the Obliquity was later on adopted by astronomers as the standard international formula.  If it had been available to Sir Norman Lockyer at this time, he would have found, instead of 1680 B.C. a date strikingly closer to Professor Gowland’s archaeological date, namely, 1822 B.C.  As it was, the good agreement between the dates found by Sir Norman Lockyer and Professor Gowland was at first received with much satisfaction by those archaeologists who believed in the very ancient date of Stonehenge.

Nevertheless, the extensive archaeological work which has been carried out at Stonehenge in recent times has made it clear that while there was an earlier blue stone circle at Stonehenge, dating back to the Bronze Age, probably about 1800 B.C., the much later great Sarsen Circle was a grand reconstruction, replacing the earlier one, but incorporating its blue stones in a new and larger design, at a time not greatly before the Romano-British period, which commenced in the 1st Century B.C., and it is probably safe to ascribe it to ancient Druid times, say between 300 and 400 B.C., when the Druids were at the height of power and influence in Britain.

Sir Norman Lockyer was impressed by the evidence for this reconstruction, although as we now see, his astronomical date, equally with Professor Gowland’s archaeological one, was much too remote.  He says (p. 95), “The theory to which my work and thought have led me is that the megalithic structures at Stonehenge – the worked sarsens with their mortices and lintels, and above all the trilithons of the magnificent naosrepresent  a re-dedication and reconstruction, on a more imposing plan and scale, of a much older temple, which was originally used for worship in connection with the May year.”

The more recent archaeological studies give a satisfactory explanation of the use at Stonehenge of old-fashioned stone axes, hammers and mauls during this period, as we shall see.

With regard to the surprising discrepancy of between 1300 and 1400 years in the astronomical date of Stonehenge found by Sir Norman Lockyer, we shall see also that, as in the case of the Solar Temple of Amen Ra at Karnak, the explanation is contained in the complete breakdown of Newcomb’s and Stockwell’s Formulae, by themselves alone, to give the true place of the Sun in ancient times.  On the other hand, we must take into consideration  the fact that the new Curve of the Obliquity does supply this deficiency which, added to these standard formulae, enables them to fulfill all the requirements of history and archaeology.  There are also many other far-reaching consequences which this implies.

In order to see this more clearly in the case of Stonehenge, let us now consider as fully as possible, first of all, a general description of the monument, and then the archaeological evidence for the date of its construction, and, finally, the astronomy of Stonehenge.  Some of this may perhaps be somewhat tedious for the general reader, but  for those who may wish to look closely into the question, it is necessary to give the available information in considerable detail, as follows.


The main features of Stonehenge are

  • The Great Circle of Sarsen Stones
  • The horseshoe formation of the Central Trilithons
  • The inner horseshoe formation of blue stones
  • The circle of blue stones, surrounding the horseshoe formations
  • The Altar Stone
  • the “Four Stations”
  • The Z and V Holes
  • The Aubrey Holes
  • The surrounding Bank and Ditch
  • The Avenue, with the so-called Slaughter Stone, and the “Friar’s Heel Stone.”

In order to understand the results of the archaeological investigations, and the astronomy of Stonehenge, we must consider these main features of the monument in detail.

Stonehenge arial

The Great Circle of Sarsen Stones

This consists of 30 immense upright stones averaging 18 feet from top to bottom, width 7 feet and thickness 3 feet 9 inches.  Their average weight is about 26 tons each.  They are let into the ground to a depth of about 4 or 5 feet, or even more, so as to bring the top of each stone to exactly the same height, 13 ½ feet above the ground.  They are arranged with their inner edges right on a circle 97 1/3 feet in diameter, according to the measurements made by the late Sir Flinders Petrie. 

These large Sarsen stones have all come from Wiltshire.  They were probably not found at Stonehenge, but the nearest site, where it is likely that they were excavated and cut nearly to shape, was in North Wiltshire, about 16 to 20 miles from Stonehenge.

The name “Sarsen” applied to these stones, is said to come from the old Saxon name of “Saracen” (Anglo-Saxon “Saresyn”), from an Arabic word meaning Oriental or Eastern, and referring to an Arabian or Mussulman, implying to the early Saxons the idea of pagan or heathen.  The “Sarsen” stones were large blocks of stones, “congregated into temples, popularly attributed to heathen worship.”

These stones are composed of sandstone, formed by the natural cementing together of sand and gravel overlying the chalk of this part of Wiltshire.  The blocks of stones at Stonehenge are very hard, so hard, indeed, that metal chisels, except of the hardest steel, would be useless for working them.  The builders worked them with crushing blows with stone mauls of quartzite weighing 50 pounds or more, and also with smaller hammers of flint or quartzite for trimming off minor irregularities. 

The spaces between individual stones average 3 ½  feet.  According to Sir Flinders Petrie’s very accurate plan and measurements, the average distance from the centre of one stone to that of the next was 10 feet 2 inches. 

The builders evidently divided the circle into 30 equal parts, and erected each stone with its centre on the point thus determined.  Slight differences in the width of stones were compensated by corresponding differences in the width of the spaces between them. 

The stones No. 1 and No. 30, on each side of the entrance on the North-East part of the monument are an exception.  They are spaced 6 inches wider apart (the actual entrance space being 4 feet wide), and the difference was adjusted by reducing neighbouring spaces on each side. 

These uprights were all surmounted by a continuous crown of great lintel stones, the adjacent ends of two lintels resting on each upright.  These lintel stones averaged 10 ½ feet in length, 3 ½ feet in width, and 2 feet 8 inches in thickness.  They weighed a little less than 7 tons each.  According to the Official Guide Book of Stonehenge, the inner face of the lintel stones was carefully dressed to the curve of the circumference of the circle to which the inner face of the uprights was a tangent.  Other descriptions indicate that the outer face of the lintel stones also was dressed approximately to the arc of its circle. 

An important architectural feature, showing a great improvement upon the design of earlier British stone monuments, is the manner in which the lintel stones were attached to the uprights.  The top of each upright was worked in such a way as to leave two conical projections, or tenons, one near each end.   On the inner side of each lintel a corresponding socket or mortice hole was ground, so as to fit accurately on the projections.  the ends of each lintel were also cut with “toggle joints,” one end with a groove, and the other with a projection.  The projection of each lintel stone then fitted exactly into the groove of the next lintel stone in the series.  The projections were triangular, and extended vertically from the top  to the bottom of the stone, and the grooves into which they fitted were also triangular, forming a deep notch vertically from top to bottom at the other end of the lintel stone.

In addition, the tops of the uprights were cut with raised edges like a shallow tray, and corresponding with these, the lintel stones were recessed at the edges to fit closely and securely on the top of the uprights.

Colonel Hawley, who examined these points closely when the lintels over the entrance stone No. 1 were re-set, found that the toggle joints fitted so well as to make it difficult to return the lintels to their former place. 

sarcen stones

The upright stones were made to taper slightly towards the top, and this taper was generally accompaniesdby an “entasis,” or slight swelling of the shaft of the column, an architectural refinement which throws light on the advanced workmanship of the builders.

In erecting the uprights, holes were dug of sufficient size to allow adjustment of the stone into its exact position.  it was then secured by packing blocks.  Some of these are known to be from Chilmark, about 13 miles distant from Stonehenge.  The holes were also provided, in all but two cases, with an incline, or ramp, down which the stone was slid.

At the bottom of each hole examined was a row of holes, sometimes six inches in diameter, suggesting the temporary use of wooden posts to steady the upright, or to assist in its adjustment to the correct position.

An important and remarkable fact, according to the official statement, is that decayed wood has been found in them.  As this is the case after so long a period, between 2000 and 3000 years, it indicates that bacterial decomposition of the wood has been exceedingly slow.

Horseshoe Formation of the Trilithons

Inside the great Sarsen Stone Circle, and symmetrically placed around the centre, are five great Trilithons of Sarsen stone, arrange in the shape of a horseshoe.  The length of this horseshoe formation along he axis line is 44 feet, and its width at the open and towards the North-East entrance of the Monument is also 44 feet.


The uprights of these Trilithons are all much higher than those of the outer Sarsen Circle.  The central one is the largest, and is known as “The Great Trilithon,” or “The Central Trilithon.”  One of its uprights is 30 feet in length, and weighs 50 tons, and the other is 25 feet long. 

Holes were made for these, sufficiently deep to allow the pair to stand 22 feet above the present ground level.  Together with its great lintel stone, the Central Trilithon rises to a total height of 25 ½  feet above the ground.  The shorter of the two uprights had a boss of untrimmed stone at the base to add to its stability. 

In their original position, there was a space of exactly 3 feet between the uprights of the Central Trilithon, from ground level to about 4 ½ feet from the top.  This will be shown to be correct later on, in the discussion of the axis of the monument, and it will be seen that it is of importance in correctly determining the position of the axis. 

It is also of importance specially in connection with the simple and unique sighting device used by the ancient astronomers for observing the exact point on the horizon, and for verifying the date of the midsummer solstitial sunrise at Stonehenge.  This is described later on in the discussion of the astronomy of Stonehenge.

The four other Trilithons are grouped in two pairs.   The height of the uprights of the pair adjoining the Central Trilithon is 17 feet 9 inches above the ground; or, adding the height of the lintels, these two Trilithons are each 21 feet 3 inches high.

The outermost pair of Trilithons have uprights 16 ½ feet high, and adding the lintels, their total height above the ground is 20 feet.

The width of the uprights of the five Trilithons was, on the average 7 ½ feet at ground level, with a taper at the top, reducing the width there to 6 ½ feet.  Their thickness was 4 feet at the ground, tapering at the top to 3 feet.

Like the Great Circle Stones, all these uprights were marked by an “entasis” treatment.  the lintel stones of the Trilithons are of an average length of 16 feet, and are 3 feet 6 inches thick; their width at the top is 4 feet 6 inches, and is reduced to 4 feet at the underside.  The top of each upright of all the Trilithons was provided, at or near the middle of its upper surface, with a conical projection, or tenon, similar to those of the Sarsen Circle stones, but longer.  Sockets or mortices were excavated on the underside of each lintel stone, so that it fitted exactly on the corresponding projection.

The Inner Horseshoe of Blue Stones

In this formation there were 19 blue stones, selected for their symmetrical shape.  They were trimmed to a kind of obelisk form with flat tops.  The heights above the ground varied from six to eight feet, with the taller ones towards the centre.

Their average width and thickness was about 2 feet.

The central blue stone, however, right in front of the Central Trilithon, was 3 feet wide,  just corresponding with the 3 foot space between the uprights of the Central Trilithon.

The purpose of this was obviously connected with the arrangement of the sighting device for observing the midsummer sunrise, previously mentioned, and to be described later.  This central blue stone was at a distance of 3 feet 6 inches in front of the Central Trilithon.  The distance of its centre from the centre of each of the adjoining blue stones on either side was 6 feet  4 inches, but the intervals from centre to centre between the other blue stones of this formation was 5 feet 4 inches.

Eleven of these stones were on a semi-circle having a radius of 20 feet from the centre of the whole Monument, and the other four on each side continued in a straight line.  There was a width of 36 feet at the outer opening or entrance of this horseshoe formation of blue stones.

Colonel Hawley, however, found indications of others, apparently completing an elliptic formation.

The blue stones of the inner horseshoe formation, and also of the circle of blue stones surrounding the Trilithons, are all of igneous origin, and do not belong to Wiltshire.  Two different kinds of blue stones were used, namely Dolerites (compact, somewhat crystalline igneous rock of a blue-green to greenish-grey colour), and Rhyolites (volcanic rock, a variety of lava, of flinty character, and dark grey colour).  It has been ascertained with certainty that they came from the Prescelly Mountains of Pembrokeshire, South Wales.  The Eastern portion of the Prescelly Mountains is rich in megalithic remains, and numerous circles of “Blue Stone” have been identified in this region.

It is 180 miles by road from Stonehenge, and whether the stones were brought into Wiltshire wholly overland, or partly by sea from Milford Haven to the River Severn, and thence overland, the transportation must have been a formidable problem, and the traditional associations connected with these blue stones must have appealed very strongly to the builders of Stonehenge.

According to old traditions, it was popularly believed that these stones possessed magical and medicinal properties.  It is possible, however, that the later builders of the great Sarsen Stone formation may have found the blue stones already brought into Wiltshire, and some think at Stonehenge itself at a much earlier date, and incorporated them into their later structure.

The Circle of Blue  Stones Surrounding the Horseshoe Formations

The stones of this inner circle are unequal in size and are imperfectly aligned to a circle about 78 feet in diameter.  They are flat stones, about 9 or 10 feet long, and they are let into the ground about 3 feet.  Their average width is about 2 ½ feet. 

The entrance stones are set well within, instead of on, the circumference, and are at a wide interval.  From centre to centre is 8 feet 7 inches. 

A great many of these stones have disappeared through depredations in the middle ages.  It has been suggested that in one of these depredations the foundations of the Central Trilithon were dug away, possibly in a search for a hoped-for buried treasure, thus leading to the downfall of the Eastern upright, and the leaning over of the Western one.

The early writers on Stonehenge thought that there were only 30 or 40 stones in the Blue Stone Circle, but  Colonel Hawley, who excavated nearly half of the Circle in 1920, found everywhere that the stones stood originally only about 18 inches apart.  The holes in which they had stood were connected by a continuous trench, in which part of a 17th Century glass flagon was found, suggesting that the trench had been dug during that period to facilitate removal of the lost stones.

He also found the actual distance from the base of the holes at the bottom, and sometimes there were broken fragments or stumps of the stones still remaining.  From the evidence which he found, Colonel Hawley estimated the number of stones in this blue stone circle to have been originally about 60.

Two of these stones of the blue stone circle have been found with cup-shaped hollows, like mortices, as if these stones had been intended to be used as lintel, and the possibility is thereby indicated that they may have been lintel stones in a circle previously in existence, and were made use of in the reconstructed design.

Both the stones of the blue stone circle and those of the inner horseshoe formation, but more particularly the latter, were worked and trimmed to shape on the spot at Stonehenge.  The stones of the blue stone circle are rough and irregular, and of various shapes.  They show signs of only a small amount of dressing, and in general are practically unhewn boulders. 

On the  other hand, the blue stones in the inner horseshoe were trimmed and dressed extensively.  In the holes which have been dug out, the quantity of blue stone  chippings was much greater than that from the Sarsen stones.  It is said they were hewed and trimmed in an extraordinary fashion, and Professor Judd estimated that they had been reduced to nearly half their dimensions in this process, the chippings almost equaling the volume of the stones themselves.

The fact that they were thus treated at Stonehenge, instead of at the place from which they were originally brought, over so long a journey of 180 miles, suggests that, in the words of Sir Normal Lockyer, they and the great Sarsen Monument “represent a re-dedication and a reconstruction, on a more imposing plan and scale, of a much older temple.”

This may have been either at Stonehenge itself, or somewhere near at hand in Wiltshire.  This problem will be further considered in connection with the “Aubrey holes.”

The Altar Stone

This is a large flat slab of micaceous sandstone, which is believed to have come from Milford Haven, South Wales, where stone of this kind is found.  It is 16 feet long, 3 feet 4 inches wide, and 1 foot 9 inches thick.  It lies flat on the ground inside the inner horseshoe formation of blue stones, and very nearly symmetrically across the axis of the monument.

It is believed that it was probably placed in a truly symmetrical position, and was displaced by the fall of the big Trilithon stones which now lie on top of it (the upper half of the broken Eastern upright and the lintel stone of the Central Trilithon).  The evidence points to the probability that it was originally placed in a flat position, the centre being 14 feet in front of the great Central Trilithon.

The Four Stations

This name has been given to two Sarsen stones, Nos. 91 and 93, and two low mounds, Nos. 92 and 94, which lie just inside the bank on, or very close to, the circumference of the circle of Aubrey holes.  It has been shown that the two mounts are the sites of Sarsen stones, like 91 and 93, which were placed originally at the centre of the mounts.

These four stones then had a remarkable geometrical as well as an astronomical character.  In the first place the lines joining 91 to 93, and 92 to 94, intersect at the centre of the whole Monument. In addition, the lines joining the inner edges of 91 to 94 and 92 to 93 are tangential to the outer circumference of the great Sarsen Circle.

Thus, on looking from 91 to 94, or from  92 to 93, these stones were completely visible from one another, and they form a rectangle, symmetrical with the axis of the Monument, and enclose the Sarsen Circle.  This geometrical arrangement seems to have been a structural feature of the original building plan, and may have been arrived at as follows:

 The distance from the outer edge of the ditch circle to the centre of the Sarsen Circle is 184 ½ feet (from sir Flinders Petrie’s measurements).  With Centre D, on the outer edge of the ditch circle, and on the axis line, a circle is drawn with radius D1C1 = 184.5 feet. 

D1S1 and D1S4 are two radii of this circle, at right angles to one another, with the right angle S1D1S4 bisected by the axis D1C1D2.

then D1S1 = D1S4 = D1C1 = 184.5 feet
and D1E = ES1 = ES4 = 130.5 feet
where E is the point of  bisection of S1S4 by the axis line D1C1D2

and S1S4 are the sites of the station stones 91, 94
and the distance between their centres S1S4 = 261 feet.
With centre C1, three circles are drawn with radii
C1G = 48.5 feet = radius of inner edge of Sarsen Circle
C1F = 52.5 feet = radius of outer edge of Sarsen Circle
C1E = 54.0 feet = radius of outer edge of Sarsen Circle plus half thickness of Station Stones 91, 94.

Then S1S4 is a tangent to the outer circle at E and the line joining the inner edges of Station Stones 91, 94, is a tangent to the outer circumference of the Sarsen Circle at F.

A rectangle S1S2S3S4 is then constructed, of which S2S3 are the sites of Station Stones 92, 93. 

S1S2 = S3S4 = 108 feet = diameter of outer circle
S2S3 = S1S4 = 261 feet

Also S2S3 is a tangent to the outer circle at J, and the line joining the inner edges of Station Stones 92, 93, is a tangent to the outer circumference of the Sarsen Circle at I.

In addition, the diagonals S1S3 and S2S4 intersect at the centre of the Sarsen Circle with angles of 45°, viz. S1C1S2 and S3C1S4, at the point of intersection.  This is a necessary consequence of the construction.

The above measurements are those of the Monument, in substantial agreement with the measurements made by Sir Flinders Petrie, and the geometrical figure provided a simple and effective means of planning the construction of the Stonehenge Circle in a symmetrical and accurate manner.

stonehenge geometry


In addition, it may be pointed out that if the details of this geometrical figure were to be measured on the ground, it would provide a simple means of checking the accuracy of the axis hereafter indicated.

The question now arises, why was the centre of the ditch circle not adopted as the centre of the Sarsen Circle?  The centre of the ditch circle is the same as that of the Aubrey Circle, but it is 2 ¾ feet south of the Centre of the Sarsen Circle, according to the measurements made by Sir Flinders Petrie.

The same geometrical construction could have been used, and the diagonals of the larger rectangle thus obtained would still have made an angle of 45° with one another at the centre, but the Sarsen Circle would have been a slightly larger one, and its diameter would have been greater than the one adopted, which was 97 feet.

Perhaps the explanation is connected with this fact, for, according to Sir Flinders Petrie’s suggestion, the internal diameter of the Stonehenge Circle, approximately 97 feet, or 1164 inches, is derived from Egypt, where it occurs generally as 1162 or 1164 British inches.  It is the diameter of a circle whose circumference is ten times the number of days in a Solar Year, in the adopted units of measurement.

The Standard Year – Day Circle was the basis not only of the Egyptian System of measures, but also of the ancient Chinese circular measure, in which the standard circle was divided into 365 ¼   degrees, to correspond with the number of days in a Solar Year. 

The ancient Egyptian standard inch is said to be equal to 1.0011 modern British inches. 

The diameter of the Stonehenge Circle, approximately 1164 British inches, would then be equal to 1162.7 primitive Egyptian inches.  If it were 1/10 inch smaller, viz 1162.6 inches, then the circumference of the circle would be exactly 3652.42 inches, i.e. the ancient Egyptian value for ten times the number of days in the Solar Year.

The internal diameter of the Stonehenge Circle is usually given as 97 1/3 feet, from Sir Flinders Petrie’s measurements; but, in view of the difficulty of measuring it exactly, it seems evident that Sir Flinders Petrie considered that the close coincidence with the ancient Year Day Circle makes it likely that the builders intended to make Stonehenge as nearly as possible this particular size, in agreement with the unique astronomical character of the structure. 

The mounds of the “Four Stations” are about 40 feet in diameter.  Each one was surrounded by a circular ditch.  Each mound covers the site of at least two Aubrey holes, and Colonel Hawley, in exploring the Southern one (No. 92) found that the ditch cuts into Aubrey Hole No. 19, and that the area enclosed by the ditch was covered by a level floor of mixed chalk and clay rammed hard.

In interment of burnt bones was found in the Northern mound (No. 94), but this is explained as the usual cremation associated with the Aubrey Holes.

With regard to the astronomical significance of the “four Stations,” the lines joining 91 (east-south-east) to 92 (south-south-east) and 93 (west-north-west) to 94 (north-north-west) are parallel to the axis of the monument.  They point to mid-summer sunrise in one direction, to the North-East, and to mid-winter sunset in the opposite direction, to the South-West.  In addition, the diagonal line joining 93 to 91 points to the position where the sun rose, in ancient times, on November 8th and February 4th.

Looking in the opposite direction, 91 to 93, the line points to sunset on May 6th and August 8th.  These four dates were “the four great festivals of the Druids,” and represented important turning points in the seasons.

These stones are not visible from one another, however, as the line of sight is blocked by the great stones of the Sarsen Circle.  If they were used observationally, it seems probable the observer would have had to stand outside the Sarsen Circle, in front of Sarsen Stone No. 6 and, looking towards Station Stone 91, he could use it for sighting purposes on a recognized point on the horizon where the sun rose on November 8th and February 4th or other positions near to it as the sun approached this point, in advance of those seasonal and festival days.

Similarly, standing outside the Sarsen Circle, and in front of Sarsen Stone 21, he could look towards Station Stone 93 to observe the position of sunset on and before the equally important season days, May 6th and August 8th.

Much interesting information concerning the ancient division of the Celtic year, and the festivals and customs connected with them, is given by Dr. J.A. MacCulloch in Religion of the Ancient Celts, 1911, p 256 etc; also by T.D. Kendrick in The Druids, 1928, pp 115-120 and 129-130; and by G.H. Bonner in an article on the Druids, in the magazine “Nineteenth Century,” September, 1925, pp. 422-430.

It was pointed out by these writers that at an early period the Celtic year was a lunar one.  But there is evidence that a solar year was later on in use.  It was, in fact, necessary for pastoral and agricultural purposes.

In their early solar calendar the Celtic year began on the 8th November, when the warm weather of summer and autumn ceased, and the cold or winter half of the year began.   The desirability of beginning the year early in November was no doubt connected with the need for bringing sheep and cattle into shelter at that time, and feeding them on stored food during the severe winter part of the year, for about six weeks before and after the winter solstice.  This early November beginning was linked with the Solar astronomical year by being half-way between the September (autumnal) Equinox and the December (mid-winter) Solstice.

The cold half of the year lasted till May 6th, when, upon its completion, the warm or summer half of the year began. 

At the middle of the cold half, on February 4th by astronomical reckoning, the mid-winter period was over, and spring was considered to begin.  This was the middle date between the December (mid-winter) Solstice and the March (Spring) Equinox.  Similarly, the 6th of May, or commencement of the warm half of the year, was mid-way between the March Equinox and the June (mid-summer) Solstice.

In the same way, the middle date between the June Solstice and the September (autumnal) Equinox, namely the 8th of August, was considered astronomically to mark the beginning of autumn.  Autumn ended, together with the end of the warm half of the year, and the winter again began, with the commencement of the next New Year on the 8th of November.

In order to mark these important dates, as well as the dates of the Solstices and Equinoxes, it was necessary for those who were responsible for the calendar to build such permanent astronomical structures as Stonehenge and any other stone, or even wooden-post structure, like Woodhenge, in many parts of the British Islands, and elsewhere in Europe, in order to observe the position of the sun on the horizon at its rising and setting points at all the important periods in the sun’s annual movement.

The application, and the importance of all the astronomical alignments of the great Stonehenge Circle, and of its “Four Stations,” can thus be easily recognized. 

Also, if the axis of Stonehenge can be determined with certainty, and if the astronomy of Stonehenge be correctly established, it must then of necessity be possible by astronomical means to determine the approximate date of its construction, in agreement both with exact archaeological and with historical evidence, if that is available.

With regard to the calendar in use at the time of the Stonehenge construction, it may be considered certain that the astronomical dates, above-mentioned, easily checked by observation from year to year, were used; bonfires were lighted on the evenings preceding the days indicating the changes of the seasons, and festivals were celebrated on the days thus fixed.

In addition, the observation of the solstitial sunrise on mid-summer’s day was the primary feature of the Stonehenge, and mid-summer’s day was marked by a special festival from the earliest times.

The mid-winter sunset, over Grovely Castle, coinciding with the prolongation of the Stonehenge axis to the South-West might also have been observed under favourable weather conditions, but no doubt owing to this difficulty much less importance was attached to it.  The modern traditional burning of the Yule log at Christmas, however, points to the survival of the age-long custom of fire-lighting in rejoicing for the anticipated arrival of longer and warmer days after the winter solstice.

The Equinoxes, too, could easily have been observed from such a unique astronomical construction as Stonehenge.  But these periods, although astronomically important, were not marked by popular festivals in ancient Celtic times.

Although the astronomical dates for the seasonal turning points in November, February, May, and August were quite definite, Dr. MacCulloch notes, nevertheless, that Beltane and Samhain, the festivals which marked the beginning of the warm half of the year in early May, and the beginning of the cold half in early November, respectively, “were perhaps at first movable festivals, according as the signs of summer or winter appeared earlier or later.  With the adoption of the Roman Calendar some of the festivals were displaced…”

In the Celtic System, as given by Dr. MacCulloch and taken from Irish texts, the division of the Year was as follows:

Geimredh (Winter half)

  • First Quarter – Geimredh, beginning with the festival of Samhain, November 1.
  • Second Quarter – Earrach, beginning February 1 (sometimes called Oimelc)

Samhradh (Summer half)

  • Third Quarter – Samradh, beginning with the festival of Beltane, May 1 (called also Cet-soman or Cet-samain), 1st day of Samono-S; Cf. Welsh Cyntefyn.
  • Fourth Quarter – Foghamhar, beginning with the festival of Lugnasadh, August 1 (sometimes called Brontroghain).

It will be noticed that in this Calendar the earlier astronomical dates in November, February, May and August have been transferred to the 1st of the month in each case.

Sir Norman Lockyer, in his book on Stonehenge (p. 181), says with regard to these astronomical dates, that there is no question that on or about those dates “festivals were anciently celebrated in these islands.”

Even as late as the tenth century, Cormac, Archbishop of Cashel, in Ireland, is quoted as saying that “in his time were four great festivals of the Druids, viz. in February, May, August and November.”

It is not certain how long the Druidic dates were used for the festivals in England, but throughout Great Britain as a whole, they were gradually displaced to the later system of dates following upon the introduction of Christianity into Britain.

The old festivals took no account of weekdays, so it was ruled that the festivals were to take place on the first day of the week; later on some of them were ruled to begin on the first day of the month.

At first there was a fixed Easter, March 22nd, and the February festival was transformed into Ash Wednesday, February 4th, when the ashes of the bonfires of the previous night (Shrove Tuesday) were made use of in connection with early Lent customs.  With the adoption of a movable Easter, some confusion occurred in fixing the dates of festivals, but there seems to have been a natural tendency to adopt the first of the month for the four seasonal festivals in November, February, May and August.

The church festival “All Hallows,” or “Hallowmass” was instituted about A.D. 610 in memory of the Martyrs, and took the place of the old seasonal festival on May 1st.  This was changed in A.D. 834 and the festival was fixed as November 1st and given the name of All Saints’ Day, in commemoration of all the saints, while the festival of All Souls, previously a commemoration of the dead on November 1st, was transferred generally to November 2nd. 

Another change that took place in the old Celtic system was the transfer of the beginning of the year from early November to the 25th March, a few days after the Spring Equinox.  This became the official date of the commencement of the year in England up till the year 1752, when the Gregorian Calendar was adopted in England.

In the same year, September, 1752, it was enacted that the commencement of the year should be on January 1st, the date which had been chosen by Julius Caesar in 45 B.C., when he rectified the Roman Calendar, and which had been accepted by Pope Gregory XIII as the beginning of the year when he inaugurated the Gregorian Calendar in 1582 A.D.

Returning to the consideration of the old Celtic calendar, preserved in the alignments of the Stones of Stonehenge, the evening before Samhain, the commencement of the year, was celebrated with bonfires.  This evening has survived in Scotland and parts of England as Halloween, the evening before All Saints’ Day, November 1st.  Samhain was a feast at which all disputes were settled.  There was also an annual commemoration of the dead, which has survived in England and other countries as All Souls’ Day. 

This commemoration of the dead was a very ancient festival, kept up at the beginning of November in many countries, including ancient Egypt, Mexico, Persia and even it is said by Australian aborigines when the Pleiades are rising in the early evenings of that month. 

In early Egypt New Year’s Day fell on November 1st, and the commemoration of the dead on that day referred to the traditional “Destruction of Mankind” in the Deluge.  This occurred, in the Genesis account, on the 17th day of the second month.

It has been suggested (D. Davidson, The Great Pyramid, p. 31) that the Genesis calendar year was an intercalated one of 360 days (each of the 12 months of 30 days duration), incalated with respect to the Autumnal Equinox; and that in the year of the Flood it began on September 16th (Gregorian date), and that the 17th  day of the 2nd month corresponded with November 1st of the early Egyptian calendar. 

In Celtic times the Druids had special ceremonies on this day.  “One of the most important was the renewing of the fire.  All private fires were extinguished on this feast, and might be re-lighted only from the sacred fire…Among other Druidic practices was that of walking around the altar in the sun-wise direction…Animals were slaughtered and food stored for the winter.”

On February 1st, at the Irish Celtic festival, Brighde, or Brigit, was worshipped as a goddess of Fire or Dew, and this date is still kept as the Irish festival of St. Bride or St. Brigit, the fires of Brighde having given place to the candles of Candlemas.  At St. Brigit’s Shrine in Kildare, “a sacred fire which must not be breathed on, or approached by a male, was watched daily by 19 nuns in turn.” (Religion of the Ancient Celts, p. 69)

The eve of May 1st, May Eve or Beltane, was a time of rejoicing at the return of the sun.  These and the other festivals were observed throughout France, England, Wales, Scotland, and Ireland and in late Celtic times they were associated with the Druids, who carried out special rites on these occasions.  It is stated that on Beltane the Druids used to make two fires, accompanying them with incantation, and driving cattle between the fires as a safeguard against diseases; while in Scotland, as late as the 18th Century, Beltane fires were lit on an artificial mound surrounded by a low circular wall, and surmounted by an upright stone, traditionally a site of Druidic worship, afterwards a place for holding courts of justice.

In many parts of England, May Day is still kept up, particularly by children, and an ancient custom survives at Magdalen College, Oxford, where, on May morning the choir sings a Latin Chant at sunrise on the top of the Tower.

Mid-summer Day, June 21st, was celebrated in Celtic times in a manner like that of Beltane.  Bonfires on Mid-summer Eve, preceding the festival day, were a central part of the proceedings, with dancing and singing, leaping through the fire, driving cattle through it to ward off disease, and in very early times, as mentioned by Julius Caesar, and other ancient writers, human victims and animals were sacrificed.

A tree had a prominent place in the Beltane and Mid-summer feasts, and was carried in procession; and,  as with the Christmas tree right up to the present time, branches of it were attached to houses.  Also a burning wheel, representing the sun, was rolled down a hill, or through the fields, or burning brands were whirled around.

In Christian times the mid-summer festival on the actual day of the solstice was replaced by the Church festival of St. John the Baptist, kept up now on June 24th, every year.  On this occasion, a sermon is preached annually in the quadrangle of Magdalen College, Oxford, during the day, as a time-honoured custom, to mark the day. 

The 1st of August, which took the place of the earlier seasonal date, August 8th, midway between Beltane (May 6) and the following Samhain (November 8) was the day when Autumn was considered to begin.  It was called Lugnasad by the Irish Celts and was an important festival throughout Britain, as well as in Europe, being the feast of the harvest.  In Roman times it was called the “feast of Augustus” and later the “August Feast.”  With the rise of Christianity it was replaced by “Lammas Day.” 

According to some writers, this name was derived from the Gaelic La Mas Ubhal, the day of the Apple Fruit; but the more generally accepted derivation is from the Anglo-Saxon Hlaf-maesse, loaf-mass, or feast of thanksgiving for the harvest.  It is still marked by festivities or fairs in parts of the country and as Dr. MacCulloch says (p. 272 of his book), “formerly assemblies at convenient centres were held on this day, not only for religious purposes, but for commerce and pleasure.”

August 1st, or rather the Monday on or following that date, is still kept in England as a national “Bank Holiday,” thus maintaining continuity with the ancient autumn festival.

The Equinoxes, in March and September, were not marked in ancient Celtic times, by important popular festivals to the same extent as the other seasonal dates, mentioned above.

Stonehenge was clearly well adapted for observing the position of the sun at sunrise and sunset at the time of the Equinoxes, and thus checking the equinoctial dates from year to year.  Nevertheless, it was not till the introduction of Christianity, with at first a fixed Easter on March 22nd that a great public festival synchronized closely with the Spring Equinox.  This close association of Easter with the date of the Equinox, however, was subsequently broken by the adoption of a movable Easter, after the coming of St. Augustine to England in 597 A.D.  This is because Good Friday and Easter Sunday had always been traditionally linked with the Jewish Passover, the date of which was calculated, not by a fixed solar calendar, but by the Jewish luni-solar calendar date of the Paschal Full Moon on the 15th day of the Jewish lunar month Nisan.

Also it had seemed desirable, and was ordained by the Council of Nice in A.D. 325, that Christians everywhere should keep the festival of Easter Day on the same date, which had been specified as “the Sunday after the first full moon falling on or after the vernal equinox,” and in that year the equinox was considered to be March 21st.

A certain amount of confusion about the date of Easter arose in later years, owing to the increasing defects of the Julian Calendar, brought into use by Julius Caesar in 46 B.C..  The Julian Calendar was used in England until the year 1752 A.D., by which time the vernal equinox had fallen back eleven days from its former Julian date. 

After the adoption of the Gregorian Calendar in England in 1752 A.D., new tables were compiled for calculating the date of Easter; and, in accordance with these tables, Easter Sunday has a wide range of dates, varying in different years between the earliest date, March 22nd, and the latest possible date, April 25th, i.e. a range of thirty-five days.  The Christian festival of Easter is therefore not a seasonal one in the sense that those of the Celtic period were.  Its connection with the vernal equinox is an indirect and an historical one, going back to the first Good Friday and Easter Day, and thence backward for 1515 years to the institution of the first Passover at the time of Moses and the Exodus.

At that time a new beginning of the Hebrew year was specially ordained, with its first lunar month Abib or Nisan, having its full moon (the Paschal full moon) on the fifteenth day of the month, on or next after the day of the vernal equinox.

With regard to the autumnal equinox (September 23), there was no important Celtic festival to celebrate it, and the nearest of the later Christian festivals is that of St. Michael and all Angels (Michaelmas Day) on September 29, associated with the Michaelmas holidays at this season of the year.

From the account of the Four Stations and the mid-summer orientation of Stonehenge, and of the great Celtic festivals at or about the dates corresponding to the various alignments, we can clearly see the astronomical importance of this unique structure, and the care taken by the builders to ensure accuracy in these alignments.

The Z and Y Holes

These are holes found outside the Sarsen Circle, as a result of Colonel Hawley’s investigations in 1920.  They are of special importance on account of the clue which they give to the date when they were dug, and thence to the date of the great Sarsen Circle. 

They consist of about 60 oblong holes, about 5 feet long and 3 feet deep.  At the bottom they are reduced to 2 to 2 ½ feet long and 1 ½ to 2 feet wide.  They are arranged roughly in two circles concentric with the Sarsen Circle, the radius of the Z circle being 65 feet, and that of the Y circle 90 feet.  Both the Z and Y holes lie directly behind and outside the uprights of the Sarsen Circle, the Z holes at a distance of 12 ½ feet and the Y holes 37 ½ feet from the outer edge of the Sarsen Circle uprights.

They contain blue stone chippings on the bottom, and some of them cut into the inclined ramps of the Sarsen holes, used in the erection of the Sarsen uprights.  This is important, because, as pointed out in the official guide book to Stonehenge (p. 23), compiled by Frank Stevens (Director of the Salisbury Museum) and published in 1938, it shows that “they were dug after the erection of the uprights.”  The irregularity of these holes is a peculiar feature, quite out of keeping with the precision of the greater portion of the monument.

Colonel Cunnington thinks they may have been originally intended, though not finally used, for the stones of the Blue Stone Circle, on account of the apparent coincidence of the number of these stones with the total number of Z and Y holes, which should be 60 altogether, though Z8 is missing and Y7 only partly dug.  There are, however, two large post holes close to the position of Z8.

On the other hand, the possibility has been suggested that they were “constructional,” and “in some way connected with the raising of the lintel stones.” (see official guide book, p. 23)  This suggestion seems a likely one.  Could they, in addition, have been used also in the process of erecting the Sarsen uprights? 

If the Blue Stones of the Blue Stone Circle originally formed the Aubrey Circle, as their number (about 60, including two probable lintel stones) suggests, might they not, after being removed from that Circle, have been temporarily used in the Z and Y holes as back stops, or anchorages, during the process of erecting the uprights, as well as the lintels of the Sarsen Circle; and, after all was complete, finally set in position in the Blue Stone Circle?

When the Sarsen uprights were brought into position, and tipped into the holes prepared for them, they would rest partly on the ramps leading into the holes, and they would project backwards at a low angle for a distance of 16 feet or more.   In this position, possibly stout poles, based upon anchorages in the Y holes, and gradually raised as the great Sarsen stones were lifted up, would be an effective support, preventing the danger of the Sarsens falling backwards through accident.

At a later stage, when the Sarsen stones were sloping at a steeper angle, shorter struts based on anchorages in the Z holes, could be used till the Sarsen stones were fully erected.  Also, in raising the lintel stones of the Sarsen Circle, some practical method of using the Z and Y holes in the process could doubtless have been used, as is suggested in the official guide book.

If the Z and Y holes were used for such a purpose, it would explain their number and the position in line with the middle of the Sarsen Circle stones, as well as their irregularity, as there would be no advantage in giving them geometrical precision for temporary constructional use.

Very important point about the Z and Y holes is the light they throw upon the date of construction of the Sarsen Circle.  For they contain a large number of broken pieces of pottery, which belong to the Early Iron Age, or Romano-British periods, between 500 B.C. and 1 A.D.

Further reference to this will be made in connection with the archaeological evidence for the date of construction.

Aubrey Holes

These are named after the celebrated 17th Century antiquary, John Aubrey, who marked on his plan in 1666 a number of ‘depressions,’ or ‘cavities’ just inside the bank.  He suggested that they might have been the site of a former circle of stones like those at Avebury.  These depressions were not visible at the time of Colonel Hawley’s investigations in 1920, but he re-discovered them by probing with a steel rod in the places marked by Aubrey.  He then excavated 32 of these sites, and found, by his excavations and probing, that there was a complete ring of holes.  the 32 excavated holes are now marked by white discs of chalk on the ground.

These Aubrey holes are on the circumference of a circle 288 feet in diameter, whose centre is about 2 ½ feet south of the centre of the Sarsen Circle.  There appear  altogether to be 56 Aubrey holes, spaced with considerable accuracy, at an interval of 16 feet 2 inches from centre to centre around the Circle.  The holes are roughly circular and, according to the Official Guide Book, they do not vary much in size or shape, being rather over 3 feet deep and 5 feet in diameter.  Most of the 32 which have been excavated contained the remains of a human cremation.  Blue stone chips and Romano-British pottery were also found in them.

There is no doubt that the holes originally contained uprights.  Archaeologists, however, are divided in opinion as to whether these were of wood or stone.  It is pointed out in the Official Guide Book (p. 18) that “the solid chalk, which lies very close to the surface at Stonehenge, has in many cases been crushed on the lips of these holes, which suggests that the uprights which may formerly have stood in them have been pulled down.”

Later on it is stated that “a very interesting suggestion has been made that the Prescelly Stones originally formed this simple circle of unwrought stones, which later on were removed and dressed to be erected in their present position within the circle and horseshoe of Sarsen Trilithons.”  If this is so, it throws much light on the question of the date of construction of the great Sarsen Circle.

Most of the holes have a ramp or incline on one side.  This descends for part of the way down the hole, and was no doubt used, like the ramps of the Sarsen stones, for putting the uprights into position. 

The cremations seem to have been placed in a shallow scoop in the upper part of the ramp, and to have slipped down, probably when the uprights were removed.  The remains are not in a compact mass, but are usually diffused downwards from near the top to near the bottom.  The cremations are considered to be dedicatory rather than sepulchral, as the bones were not always sufficient for a complete body, and no relics were found with them. 

The central portion of the filling in of the Aubrey holes was found to be usually more earthy than the edges, and contained late relics, such as Romano-British pottery, to a greater depth.  No stone chips were found at the bottom of the Aubrey holes.  This is regarded as evidence that the Sarsen Stones and the Blue Stones had not been chipped when the Aubrey holes were filled (see Stonehenge and its Date, R.H. Cunnington, 1935, pp. 26, 28).

Surrounding Bank and Ditch

The area on which the Stonehenge monument stands is surrounded by a circular Ditch, with a low Bank adjoining it on the inner side.  The circles of the Ditch and Bank were drawn with precision, and they must have been constructed before the Sarsen Stones were erected.  Otherwise it would have been impossible to use a picketed cord to draw the circles. 

The centre of both Ditch and Bank is the same as that of the Aubrey circle, 2 ¾ feet south of the center of the Sarsen Circle.  The radii are as follows:

Outer edge of Ditch – 187 feet
Junction of Ditch and Bank – 168 ½ feet
Center of Bank – 159 ¼ feet
Inner edge of Bank – 150 feet

The top of the Ditch and the Bank are therefore both of the same width, viz. 18 ½ feet. 

The Bank is now greatly worn down, and the Ditch is more than half filled up.  The mean height of the Bank above the general level of the enclosure is only 14 inches, and the bottom of the Ditch is now 2 feet 3 inches below this general level.  It is considered that when freshly dug, the Ditch was between 4 and 5 feet deep and 6 or 7 feet wide at the bottom.  As the width at the top is 18 ½ feet, this gives a slope of about 37 degrees.

From experience in the silting up of ditches, it is considered that the Ditch silted up rapidly at first, a great deal of the coarse silt at the bottom being due to the thawing of frozen surfaces in winter mornings, causing disintegration and slipping of the chalky fragments to the bottom.  After that, fine chalky material would be washed down and would form a thin layer above the coarse silt. 

This process has a bearing on the archaeological relics found in the Stonehenge Ditch.  The top layer now consists of an earthy chalk rubble 15 to 18 inches thick, including the modern turf.  Below this are a few inches of fine silt, “divided abruptly from the top layer,” and then there is about a foot of coarse silt at the bottom.

The main entrance on the north-east side was originally a causeway, 37 ½ feet wide, where the Ditch was never dug.  there was another causeway, called the Southern Causeway, almost exactly south of the monument, where also the Ditch was not dug.  This was probably a ceremonial entrance, as it is exactly in line with the short Sarsen Stone No. 11, which was not provided with a lintel.  The suggestion has been made that this was to allow processions with banners to enter the Sarsen Circle.

With regard to the north-east Causeway, it appears that very soon after the Ditch was dug, the last 30 feet were filled up with clean white chalk, rammed hard.  This shows that the fillings had been intentional, in order to widen the entrance, and to make it nearly the same as the Avenue, which is 71 feet wide.

Colonel Hawley found in his excavations that where the original digging of the Ditch ended, there was a nearly perpendicular wall of solid chalk, 4 feet 9 inches high.  It is evident that this part of the Ditch was filled up again very soon after it was excavated, and before silting had begun, as there are no signs of any earthy mixture in the filling.

No doubt the Causeway was left intact to provide an entrance through which most of the great Sarsen Stones may have been transported, and in connection with the transportation a wider entrance may have been found desirable; hence the hard ramming of the material; and, in addition, it was then symmetrical with the Avenue of which the complete construction was probably a later stage of the work.

The Avenue, Friar’s Heel Stone, and Slaughter Stone

The Avenue

This is a broad, prehistoric roadway extending from the Monument, at first for nearly 600 yards in a straight line to the North-East (the direction of mid-summer sunrise), from the outer edge of the Ditch.  The central portion is 47 feet wide and is slightly raised above the general level.  On each side of this central road is a low bank rising from a shallow ditch.  These two ditches are now each about 12 feet wide, and about 2 feet deep.  Excavation has shown that the ditches were originally constructed in a V- shape, and were then about 3 feet deep.  They are 71 feet apart from centre to centre.

The ancient Avenue takes a slight downward course, with the general slope of the land, until it reaches the bottom of the valley.  Then it divides into two branches; one branch turns upwards in an easterly direction, and goes toward Amesbury, 2 ½ miles distant.  The other branch goes to the left, and is believed to join up with the “Cursus,” a large oval area which is considered to have been possibly an ancient race-course, or ground for contests and sports.  A suggestion has been made that it may also have been used for prehistoric fairs, or as a market place.

On approaching the circular Ditch of Stonehenge, the banks and ditches of the Avenue become shallower, and cease within 10 feet of it.  The central line of the Avenue passed centrally between the entrance stones Nos. 30 and 1, of the Sarsen Circle, through the centre of the Circle, and midway through the uprights of the great Central Trilithon. 

It will be shown later on to be correct, and is of importance, as being the true axis of Stonehenge.  It is clear that this central line was intentionally directed towards the point of mid-summer sunrise, when the Stonehenge Sarsen Circle was built.

The Friar’s Heel Stone

This is a very large Sarsen stone, rising to a height of about 16 feet above the ground.  It is 8 feet wide near the centre, but tapers to a blunt point at the top.  It is about 4 feet thick, and is set in the ground in a position leaning toward the monument.  It is situated in the Avenue about 6 feet to the right, or south-east, of the central line, and at a distance of 256 feet from the centre of the monument.

Various explanations have been given about the name, but the most likely seems to be that it was derived from the original Celtic name “Cloch Na Freas Heol,” or “Stone of the rising Sun.”  Of course, it is not in line with the point of sunrise as seen from the centre of the monument; and in ancient times it must have been nearly 1 ¼ degrees east of the point of sunrise, indicated by the direction of the axis and the central line of the Avenue. 

When the sun had fully risen above the horizon, there would have been a certain position inside the Sarsen Circle, from which the sun would appear at that moment vertically above the Friar’s Heel Stone.  On the other hand, it may have been used as a gnomon for casting a shadow, the position of which was observed, on and near the day of the summer solstice. 

Thus E. Duke, in his book Druidical Temples, 1846, p. 133, says “it was a gnomon for the purpose of observing the rising of the sun on the auspicious morn of the summer solstice.”  Reference to this will be made in connection with the Astronomy of Stonehenge.

In the Official Guide Book of Stonehenge, by Frank Stevens, p. 21, it is said that “Further indication of the importance of this stone, to the builders, was forthcoming when excavation on the western side revealed a circular trench about 30 feet in diameter surrounding it.  The eastern portion of this had been destroyed by the present-day roadway.”

Slaughter Stone

This is a large block of Sarsen lying flat and partly embedded in the ground.  It is about 6 feet east of the axis, and 150 feet from the center of the monument.  It lies lengthwise nearly parallel to the axis, and its length is 21 feet 6 inches, width 6 feet 9 inches, thickness 2 feet 9 inches.  It has evidently been misnamed, as it has been shown that it stood erect about the middle of the 17th century, and that it formed one of a pair of great Entrance Stones. 

The hole in which the companion stood was excavated by Colonel Hawley in 1920.  Its centre was about 8 feet 6 inches from the nearest part of the Slaughter Stone on the north-west side, and about 152 feet 6 inches from the centre of the Sarsen Circle, i.e. just on the Bank, and not far from its inner edge.

Colonel Hawley reported that “We came upon a very large hole roughly 10 feet in diameter by 6 ½ feet deep which we gradually excavated.  We found a coin of Cladius Gothicus in the upper layer, but nothing interesting until we reached the bottom where two Deer Horn picks were resting against the side.  There can be no doubt that a large stone once stood in the hole.” (Note Claudius Gothicus was Roman Emperor from 268-270 A.D.)

The earliest print of Stonehenge, dated 1575 A.D., shows two large stones within the circular earth work, one on each side of the entrance.  These are also confirmed by the reports of Inigo Jones, about 1621, and John Aubrey, 1666, who also indicate a smaller pair of upright Entrance Stones in addition to the larger ones.  In Aubrey’s time, however, one of the smaller of these four stones seems to have been missing.

The Archaeology of Stonehenge

The archaeological investigations at Stonehenge, which have been very extensive, have led to remarkable divergences of opinion regarding the date of its construction.

Before going farther into this question, it should be made clear that, whether or not there was an earlier blue stone circle in existence before the great Sarsen Circle was built, it is the date of the latter, and its axis, which are essential considerations from the point of view of the astronomy of Stonehenge.

In the 17th century, Aubrey, Stukeley, and others were strongly convinced that Stonehenge was a Druidical Temple, and this was the general belief in the 19th century.  Later investigators, however, increasingly favoured a much earlier date, and interpreted the evidence to correspond with the late Neolityic or Early Bronze Age, with the date about 1800 B.C., or perhaps Middle Bronze Age, about 1200 B.C..

The fact that stone hammers or mauls were used to work the Sarsen Stones, and Deer Horn picks were used for digging, seems to support a very early date.  But it has been pointed out that metal chisels would have been too soft to work such hard stone as the Sarsen Stones and Blue Stones; and tools of flint and quartzite were the most effective.  Also, for digging, Deer Horn picks would have been used at any time, and are even in use nowadays in isolated parts of Scotland.

In support of the very early date, the analogy with numerous ancient Megalithic structures in the British Isles, and on the Continent, seemed to point to an equally early date for Stonehenge.  On the other hand, however, it has been shown that the architectural character of Stonehenge is far beyond that of the early Megalithic structures, and is more characteristic of the later period.

Sir Norman Lockyer’s astronomical investigations in 1901 supported the early date for Stonehenge, and aroused great interest in archaeological circles.  This will be considered in detail in the next section, relating to the astronomy of Stonehenge.

Archaeologists in general admit that the axis of Stonehenge must have been intentionally aligned to the position of the sun at sunrise on the day of the summer solstice.  Consequently, the astronomical date found by Sir Norman Lockyer carried much weight with those who interpreted the archaeological data as pointing to the building of Stonehenge at the end of the Neolithic period, or the beginning of the Bronze Age; and up till 1925 this was a common opinion amongst archaeologists.

But in 1920, Colonel Hawley’s excavation brought to light a great deal of fresh material which, as time went on, and as the evidence was more thoroughly studied, brought about a change in the archaeological outlook.  The evidence has been set forth in detail by Colonel R.H. Cunnington in his book Stonehenge and its Date, published in 1935.   The conclusion which he reaches is that the large amount of Iron Age and Romano-British pottery found at Stonehenge leads to the belief that the date of construction must be brought down to the “Iron Age of the Celts and the 4th and 5th centuries B.C.”  for a full account of this evidence, reference may be made to Colonel Cunnington’s book, but the following brief notes will serve to indicate its nature.

First of all, we had better give some indication of the approximate dates of the various periods, or ages, recognized by archaeologists in their dating of the specimens of pottery and other materials found at Stonehenge.

The first period, to which the earliest of these specimens are generally referred, is the Neolithic, or “new” Stone Age, marked by certain kinds of stone implements, pottery, and sepulchral relics.  This period ended about 1800 B.C., when England was invaded by the “Beaker Folk.”  These “Beaker Folk” came from the Continent, and spread inland through the Southern and Eastern parts of England.  Wherever they went, traces of them are found in the “Beakers,” or drinking cups, which they made of the local clay.  Specimens of this prehistoric pottery are widely distributed.  They also  introduced bronze weapons, and other articles made of bronze, and this introduced into England the “Bronze Age.”

The Early Bronze Age is considered to last from about 1800 B.C. to 1500 B.C..  The Middle Bronze Age may be considered as the period 1500 B.C. to 1000 B.C., and the Late Bronze Age from 1000 B.C. to about 700 B.C.  It then overlaps the beginning of the Iron Age, when the use of iron was introduced into Britain.

The Iron Age in Britain, before the coming of the Romans, is subdivided into three periods, known as Iron Age A, Iron Age B, and Iron Age C.  Iron Age A is considered to commence about 700 B.C.  This earliest division of the Iron Age is also known as the Hallstatt period.  The name is derived from the village of Hallstatt, in the Austrian Tyrol, where a large deposit of the earliest Iron Age relics was brought  to light. 

The date of the arrival of the Hallstatt invaders in large numbers into Britain is considered to be not much earlier than 600 B.C., though their influence was felt some time before that date. 

The period from 500 B.C. to the beginning of the Christian Era includes the two later sub-divisions Iron Age B and Iron Age C.  It is also called the La Tène period.  This name is taken from a site on Lake Neuchatel in Switzerland, where typical relics of these people were identified.  It is marked by new types of weapons and ornaments, and by new kinds of pottery.   These La Tène people are identified as the early Celts, who were known to the Greeks about 500 B.C.

It is established that by this time numbers of them from the lower Rhine had found their way to the Pyrenees and North Spain, which was linked with the South-West part of Britain by the tin trade.  Many came to England by this route, but the greater numbers moved through France and Brittany, and invaded England from Brittany in the 4th century B.C.  They were very vigorous people, and it is said that the La Tène Celts dominated, while mixing with the native population.

Iron Age C commenced in the 1st century B.C., with the invasion of England by the Belgae, from Belgic Gaul.  The Romano-British period is included in Iron Age C, and continues in Roman times. 

It should be pointed out that pottery, and other articles characteristic of these various periods may precede the invasion date, on account of the influence of Continental trade.  Also, articles typical of certain Ages may have been used at later periods owing to survival.  Thus, during Iron Age A “there was a survival in certain regions of the flint industry.”  Numerous types are mentioned, including “hammer stones and pounders,” also “picks of Deer Antler occur.” (See Archaeology in England and Wales, by Kendrick and Hawkes, 1932, pp. 167-168).  This has a bearing on the occurrence of such articles at Stonehenge.

The following is a brief account, chiefly taken from Colonel Cunnington’s work, as well as from other sources, of the archaeological evidence found at Stonehenge, giving a clue to the date of its construction.

The Ditch and the Bank:  Mention has already been made of the rapid silting of the ditch after it was first dug, with coarse silt at the bottom, about one foot in thickness, overlaid by a few inches of fine silt, this being divided abruptly from the top layer, “consisting of earthy chalk rubble, 15 to 18 inches thick, including the modern turf.  The silt contains very few relics; some animal bones, and worked flints, two small scraps of unidentified pottery, and at the bottom a number of Deer Horn picks, and roughly chipped flints.”  Colonel Hawley excavated 180 feet of the Ditch, and the few relics found in the silt do not throw definite light on the date.

The flints and Deer Horn picks have been considered by some archaeologists as evidence of Neolithic or Bronze Age date, but from what has been established about the use of flints and Deer Horn picks in the early Iron Age, the presence of these articles does not necessarily imply an earlier date.

Some small scraps of Beaker pottery were found lying on top of the fine silt, and partly embedded in it, but these are not sufficiently numerous to be regarded as sufficient evidence for Bronze Age construction, as occasional fragments of this pottery are found almost anywhere in the soil of Salisbury Plain, where extensive excavations have been made.

The Official Guide Book mentions a “small late Bronze Awl, c. 500 B.C. (the only actual Bronze Age implement yet found).”  This was found in the earth above the chalk silt.  It might, of course, be of a later date, by survival , but not an earlier date than the period to which it belongs.

The top layer of the Ditch, representing the growth of turf after silting, together with the accumulation of soil for many centuries, contains numerous relics, including pottery of all Ages from early Bronze to Romano-British.  In addition, stone chips are plentiful throughout this layer.

In the 180 feet of the Ditch excavated by Colonel Hawley, 19 sections were dug, and Romano-British pottery was found in every one of them.  A remarkable thing is the “almost complete absence of anything later than Romano-British.”  This shows the relative frequency of visitation by the people of the Romano-British period, as compared with those who came after them, right up to modern times.

The total of each kind of pottery is as follows:  “Norman pottery, 3; Romano-British, 136 in 17 sections, and some in the other two, or say 145 in all (excluding the fragments of a New-Forest-ware pot, which were found together); coarse ware generally described as earlier in date, 36; coarse black ware found in one section, and described as mostly of the Bronze Age, 30; Bronze Age, 6; Beaker, one in the top layer, and the two associated groups, (of 10 and 12 small pieces), already referred to, lying on the silt.”

Colonel Cunnington comments that the definite Bronze Age pottery is scanty, no more than might have been found in any soil in the neighbourhood, and the chief ingredients are the unspecified or doubtful coarse ware, and the Romano-British.  He thinks it likely that the “coarse ware of an earlier date” may be early Iron Age, and that it occurs generally at the lower level than the Romano-British.

Most of the pottery in the top layer of the ditch ranges from Iron Age A to Romano-British, and “there are no grounds for supposing the top layer is earlier than that in date.”  He also points out that several cremations were found in the Ditch, most of them in the silt, and therefore later than the Ditch.  There was one, however, on or sunk into the floor without any signs of being an intrusion, which seems to have been contemporary.  Since cremations are not known until after the Early Bronze Age, it affords evidence of a later date.

The Bank has not been archaeologically excavated, except for two narrow trenches cut through it and the Ditch.  The Bank is, therefore, a promising field for future exploration.  Surface soil inside the Bank is described as similar to the top layer of the Ditch, containing relics of all dates jumbled in any order.  The great quantity of Romano-British pottery found here is commented upon by Mr. Kendrick. As he says, it is “Far more than one would expect from trippers visiting the site to look on a ruin.”  That is to say, that in early Roman British times Stonehenge was at the height of its fame and use, and therefore is not likely to have been built more than a few centuries earlier.

The Bank was evidently made from the earth originally thrown out when the Ditch was dug.  Allowing for the wearing down of the Bank by some 4 or 5 inches during the centuries since it was made, the cubic contents of the Bank at the time of its construction would agree with those of the Ditch.

An important point, throwing light on the relative dates of construction of the Bank and Ditch, and of the great Sarsen Circle, is that which has been mentioned previously in the description of the Ditch.  For the widening of the North-East Entrance Causeway over the Ditch, by an additional 30 feet (from 37 ½  feet to 67 ½ feet), very soon after the original digging of the Ditch to that point, and its obvious purpose to give more room for the transportation of the great Sarsen Stones into the Stonehenge enclosure, shows that the Ditch and Bank must have been constructed at the same date, and as an immediate preliminary operation before the Sarsen Circle was built.  The correct dating of the Ditch, therefore, would help us in determining the date of building the Sarsen Circle.

Aubrey Holes:   Colonel Cunnington says that there is little evidence of date in the Aubrey Holes.  Nothing datable was found near the bottom, and only a few relics were in the upper layer.  Romano-British pottery might occur as low as 2 feet below the surface, or 8 or 9 inches below the level of the surrounding solid chalk.  It seems probable that the holes were not filled in with tightly packed material, as the depressions were noticed by Aubrey in the 17th century. 

In the succeeding two and a half centuries, however, these depressions became filled up, so that they were only found by Colonel Hawley by probing in positions as indicated by Aubrey’s plan of 1666 A.D.  In the Official Guide Book it is said that

Among the finds in the Aubrey Holes were ‘fabricators’ of flint, used in the manufacture of flint implements, and flint flakes; some of these have been replaced upon the cores from which they have been struck off, showing that the work was done on the spot.

Besides these there were axes and hammers of Prescelly stone, and fragments of Bronze Age pottery.  One of these is of special interest; it is a portion of a vessel with perforated lugs, which may have been an ‘Incense Cup’ of the Middle Bronze Age.

A picture of this “Incense Cup” from the Aubrey Holes is given on page 39 of the Official Guide Book.

Amongst the cremations around the Aubrey Holes there were “bone pins, well finished, some bearing traces of fire, and a beautifully finished Bronze Age Mace-head in hornblendic gneiss, a stone foreign to the district but found in Brittany and also in Scotland.  This shows no trace of wear, and might, therefore, have been ‘ceremonial.’”

In the ground between the Outer Sarsens and the Aubrey Holes the following archaeological specimens are listed:

Roughly chipped flint implements, Bronze Age pottery, Early Iron Age pottery (c 400 B.C.), pottery “counter” or disc for playing some game, three Roman coins, Roman fibula (A.D. 350 – 400), Roman toilet article, Anglo-Saxon silver belt ornament, coin of Ethelred II minted in London, Norman harness ornament, a groat of Henry II, cut to make a half-groat, and small bell pendant, possibly from a horse trapping.

Z and Y Holes:  These contain a large number of fragments of Romano-British pottery, with a much smaller proportion of Bronze Age pottery.

In the Z holes the total number of fragments of Romano-British pottery enumerated by Colonel Hawley is 190,  and of Bronze Age pottery, 27.

In the Y holes there were 206 fragments of Romano- British pottery, and 35 Bronze Age fragments.

Thus in both Z and Y holes the Romano-British specimens out-number those of the Bronze Age by about 6 to 1. Some of the pottery fragments included under the heading of Romano-British, however, have been identified as La Tène.

An important find, bearing on the date of the Z and Y holes, was the grave of a La Tène man, near one of the Y holes, Y11.  This has been referred to by Mr. T.D. Kendrick as a definite evidence of the late construction of the monument.

Number of Pottery Fragments of Various Ages

An analysis of the fragments enumerated by Colonel Hawley, in his excavations at Stonehenge between the years 1919 and 1926, covering about half the Stonehenge area, gives the following total number of various kinds of pottery, which he found, excluding the modern period, which was not tabulated:

Bronze Age, including “Beaker” or Early Bronze Age pottery – 250
Early Iron Age, prior to the Romano-British period – 85
Romano- British – 925
Norman and Mediaeval – 116

Total = 1376

These figures show, first, that Stonehenge was greatly frequented in the Bronze Age.  This is to be expected, as in the immediate neighbourhood of Stonehenge there are about 300 round Barrows, or ancient sepulchral mounds.

Frank Stevens points out in Stonehenge Today and Yesterday, p. 47, that

they seem to crowd about the Circle as do the graves in a country graveyard around the Church.

This can hardly be accidental; rather would it appear that the Barrows reached their highest development on Salisbury Plain and the Stonehenge region, and formed a vast necropolis about the circle…. They justify the assumption that the sanctity of the site made the spot specially attractive for burial.

The Round Barrows are typical burial mounds of the Bronze Age.  There are only two Long Barrows, characteristic of the Neolithic period, near Stonehenge; but it is to be pointed out that the round Barrow does not belong exclusively to the Bronze Age.  In Archaeology in England and Wales, 1932, p. 109, the authors, Messrs. Kendrick and Hawkes, say of the Round Barrows that “Some were erected in the  Early Iron Age, some in the Roman period, and some in Saxon and Viking England.”

Thus they persisted for a long time, though they were specially associated with the Bronze Age; and an account of this predominantly Bronze Age character, the presence of so many of these Round Barrows and the considerable amount of Bronze Age pottery found in the Stonehenge Area, is consistent with the opinion of many archaeologists that, before the present monument, there was an earlier one, namely, a circle of rough or unhewn blue stones, brought over from South Wales during the Bronze Age.

The preponderance of Romano-British pottery fragments at Stonehenge, with a small number of Early Iron Age fragments, suggests the probability of a reconstruction in the present form at a period not greatly before the Romano-British times.  If the reconstruction took place a few centuries before the Romano-British period, say between 300 and 400 B.C., it would explain both the occurrence of pottery of the Early Iron Age, La Tène period, and also that of the Romano-British period, during which it reached its maximum use and importance.

Other Evidence

Climatic conditions indicated by snail shells

Colonel Cunnington also makes use of the evidence of the snails which are found at Stonehenge.  He refers to the practice of excavators of prehistoric earth works,

in submitting samples of earth for analysis of their snail shell contents.  The snails are very small, almost microscopic, and belong to a large number of species, some of which like damp conditions, and other dry; and, by counting the number of each, it is possible to say what the climate was like when the earth work was made, and whether the surroundings were open down land or wooded.

From this kind of evidence, which is very consistent, “it seems safe to say that the Neolithic and Early Bronze Age in the South of England was decidedly wetter than now, and all the earth works at that time must have the damp-loving snails.”

From that time onwards, the climate was becoming dryer.  At Stonehenge, “several samples of earth were taken from the ditch and from the post holes, and in all of them was a total absence of the damp-loving snails.”  This indicates that the conditions were those of a dry climate, the same as today, and that the Ditch, and other major works accompanying it, namely the Bank, the four Stations, and the great Sarsen Circle itself, with its interior great Trilithons and other unique features, were constructed at a comparatively late period, and not in the Neolithic or Bronze Ages.

Architecture of Stonehenge

Mr. T.D. Kendrick, in his book the Druids, discusses the architecture of Stonehenge at some length.  He describes Stonehenge as “an architectural achievement that is completely beyond anything hitherto attempted in the ordinary megalithic tradition.”   

Besides special methods of cutting and trimming the great Sarsen stones, the builders of Stonehenge “employed a new device unknown in the megalithic architecture of Europe.”  This was the classical method used in temple building in Greece and Rome for assembling the members of a column by the “peg-and socket lock.”  This is seen in Stonehenge in the mortice and tenon method of securely fastening the lintel stones to the uprights, both of the great Sarsen Circle and of the horseshoe formation of Trilithons inside the Circle. 

Mr. Kendrick says, “I repeat therefore that the mortice and tenon betray the indirect influence of classical architecture, and bring the date of the monument down to the La Tène period.”  He supports this argument from another equally strong point of view, concerning the religion of Druidism. 

By Druidism he means the early Celtic religion introduced into Britain by the La Tène people, identified with the early Celts, who invaded Britain in large numbers from the region of the lower Rhine, from about the year 500 B.C. and onwards.  He says in The Druids, p. 155,

If Stonehenge was not a temple of Druidism, then it must have been a disused ruin in the La Tène period when druidism was the religion of the land.

But does all the British and Romano-British pottery and the actual burial of a La Tène man within its area (Antiquaries; Journal V. 31) really suggest the visit of trippers to look at a ruin?  I think not.  And I would ask what was the religion of this La Tène man, this early Briton who was buried there, if it was not druidism? 

And if it was druidism, is it not more likely that a believer would be laid to rest in the temple-precincts of his own faith than in the ruined sanctuary of a forgotten religion?

To sum up – the sequence of events at Stonehenge, most likely from the foregoing archaeological results, and from the comments of various learned authors, seems to be first, that there was a simple blue-stone circle, with lintel entrances, first of all established in the Bronze Age; and the site of it was that of the Aubrey Holes.  The centre of this circle was 2 ¾ feet south of the centre of the later Sarsen Circle.

This blue-stone circle lasted for about a thousand years, and was used in the religious system of the ancient Britons, before the Celtic or La Tène invasion.  These newcomers, upon obtaining domination in Britain, subsequently, i.e. between about 300 and 400 B.C., re-constructed the ancient temple, in a different form, a part of a new and impressive temple, in the following orders:

  1. The old blue-stones were removed from the Aubrey site.
  2. The circles of the Ditch and the Bank were marked out on the ground, having the same centre as that of the original blue stone circle, i.e. the Aubrey circle of today.  (The ditch was dug with, at first, an entrance to the Circle area inconveniently narrow for the transport of the giant Sarsen Stones, and this was widened soon afterwards, before silt had time to form.  The Bank was formed from the material thrown out from the Ditch.)
  3. The geometrical working plan for the construction of the great Sarsen Circle was carried into effect.  This was based on the dimensions of the ancient Standard Year-Day Circle, and the plan of this Circle was associated with the provision of the “Four Stations,” designed for the exact astronomical observation of the position of the sun at sunrise and sunset on the four great seasonal and festival dates of the ancient Celtic year, corresponding to our February 4th, May 6th, August 8th, and November 8th.   This geometrical plan further necessitated the centre of the Sarsen Circle being 2 ¾ feet north of the centre of the Ditch and Bank circles.
  4. The main axis of the monument, pointing in one direction, North-East, to the midsummer sunrise point, and in the opposite direction South-West to the mid-winter sunset, was secured by making it coincide with the middle point between the entrance stones 30 and 1, to the North-East, and to the middle point between their opposites, 15 and 16 to the South-West.
  5. The accuracy of the observation of the mid-summer sunrise, in the line of this axis, was further secured by building the great Central Trilithon with its central aperture exactly centred on the axis line.
  6. The other great Trilithons of the horse-shoe formation, together with the inner horse-shoe of blue stones, and circle of blue stones surrounding these horse-shoe formations, were erected at the same time; probably using the blue stones of the ancient Bronze Age temple, with a small amount of trimming for the latter circle, and blue stones from some other source, either Wales or possibly an existing circle near at hand, after much trimming and dressing, for the inner blue stone horseshoe.
  7. The Avenue, with its side ditches, was finally constructed in such a way that its central line exactly coincided with the axis of the monument, and was directed with accuracy towards the mid-summer sunrise point over the summit of Sidbury Hill.

The provision of this long axis line of the monument and the Avenue, so accurately directed towards the mid-summer sunrise, as seen from Stonehenge, is the chief point of importance in the astronomy of Stonehenge.  Therefore, while it is of great interest, and necessary for understanding the problem of Stonehenge, to examine its archaeological and historical data as a whole, the remainder of this enquiry will be devoted first of all to the study of the various attempts to define the true axis of Stonehenge, and then to show that, if the astronomy is also truly established, we shall necessarily obtain from it a result for the date of construction of the great Sarsen Circle and its adjuncts in close agreement with both the archaeology and the history of the monument.

Finally, we shall then see that the astronomy of Stonehenge, equally with that of the Great Solar Temple of Karnak, shows clearly that whereas Newcomb’s Formula gives a completely unacceptable and erroneous building date for each of these famous monuments of antiquity, the New Curve of the Obliquity of the Ecliptic, which has great implications also in other directions, does give that necessary agreement both with archaeology and with history. 

For in addition to the general historical background outlined in the preceding pages, we have the following specific and striking reference to the rebuilding of Stonehenge somewhere about the year 350 B.C. by the celebrated early British King Belinus.  This is given by R.W. Morgan in his History of Ancient Britain.  He says that King Belinus (who was the brother of Brennus, who sacked Rome in 390 B.C.)

after the conquest of Germany, founded Aquileia, where he was afterwards worshipped as a god.  Returning through Gaul he divided his territories amongst his five younger sons, retaining the government of Britain alone in his own hands.  He employed the latter years of his long and glorious reign in peaceful legislation and the construction of public works. 

Belen’s Castle (Billing’s Gate) and the stupendous embankment of the Thames were begun and completed under this monarch.  He built also Caer leon (originally Caer usc) and repaired the Druidic Temples of Cor gawr (Stonehenge) and Ambri.  He died in the 80th year of his age.  His body was burnt and the ashes deposited in a golden urn on the top of the highest tower of his palace on the Thames.

According to this, the re-construction of Stonehenge would thus have been carried out somewhere about 350 B.C.

The Astronomy of Stonehenge

There can be no doubt that Stonehenge,  in addition to its other purposes, was designed for astronomical use, associated with maintaining the ancient Calendar, since it has those remarkable alignments of the main axis and the “Four Stations,” all definitely directed towards the position of the sun on the horizon, at sunrise or sunset, on the most important seasonal and festival days of the Celtic year. Of these alignments, that of the main axis of the monument, directed to the mid-summer sunrise point on the North-East  horizon, and to mid-winter sunset in the opposite (South-West) direction, is the one upon which an astronomical determination of the date of construction of the great Sarsen Circle can be accurately based, provided that we can be sure of the true position of the axis.

This axis, however, has not been easy to define with the desired certainty, owing to the present imperfect condition of the monument.  Four attempts have been made, and with four different results.  We must now enquire into the question of their accuracy.  Then, further, we must examine the astronomical basis on which a determination of date can be made.

Petrie’s Axis:  The first of the four attempts to define the axis of Stonehenge, which we shall consider, is that which was made by Sir Flinders Petrie in the year 1877.  He measured the position of all the standing stones, and included on his plan five other stones standing in 1747, whose positions were taken from Wood’s plan of that date.  He then drew a “mean circle” which, he thought, “agrees best to all the Sarsen stones, making allowance for their shiftings.”  Petrie’s Axis was fixed by him as follows:

  • The middle of the entrance, between stones 30 and 1
  • The centre of his “mean circle.”
  • The centre of the space between “the assumed original place of the great trilithon stones 55 and 56, considering that they have slewed northwards in falling; the assumed distance between them, eliminating the slew, is 13 inches.”  This, he says, “closely agrees with the standing trilithons which are 12.8 and 12.4 inches.”  (Thus, Petrie’s axis passed approximately 6 ½ inches from the side of the leaning Central Trilithon stone No. 56 as it was in 1877.  An adjustment of this measurement to the present position of No. 56, restored to verticality in 1901, makes Petrie’s axis 8 inches from No. 56 as it is now.)
  • Half the average spacing between the stones allowed from the side of No. 16; this is very vague as the interval varies from  26 to 51 inches; the mean, being 36, gives 18 for the half distance.”

When this axis line is produced, it differs markedly from the central line of the Avenue.

At the Friar’s Heel Stone it is 1 foot 10 inches to the East of the central line of the Avenue, and strikes the Heel Stone 10 inches within its left, or North-West side.  It then continues to diverge farther from the central line of the Avenue at the rate of about 11 inches in every 100 feet.  This large divergence of Petrie’s axis from the direction of the Avenue shows that Sir Flinders Petrie failed to recognize that the Avenue, as it leaves the monument, was itself truly directed towards the mid-summer sunrise point at the date when Stonehenge was built.

It was, in fact, an integral part of the whole Stonehenge axis system; and it will be shown that it was a true prolongation of the internal axis of the monument.  This was realized and demonstrated by Mr. E.H. Stone in his book The Stones of Stonehenge, published in 1924.

The complete axis system of Stonehenge, defining both the position of mid-summer sunrise to the North-East, and midwinter sunset to the South-West, at the date of construction of the Sarsen Circle, is seen to be a line, 14miles altogether in length, from Grovely Castle, 6 miles South-West of Stonehenge (marking the position of midwinter sunset as seen from Stonehenge), passing through the Sarsen Circle

  1. midway between the south-west stones 15 and 16
  2. midway between the uprights of the Great Central Trilithon
  3. through the centre of the Sarsen circle, and thence
  4. through the middle of the space between the entrance stones 30 and 1
  5. then along the centre line of the Avenue toward the ancient Sidbury fortification on the summit of Sidbury Hill, 8 miles north-east of Stonehenge, where the sun, as seen from the monument, rose on midsummer day at the date of construction of the Sarsen Circle.

This was clearly recognized by Sir Norman Lockyer, in his account of Stonehenge; and the very slight difference in the azimuth angle of the two extremities (49⁰ 34’ 18” East of North for Sidbury, and 49⁰ 35’ 51” West of South for Grovely Castle), quoted by him from the Ordnance Survey, is not more than is to be expected from  slight differences in the altitude of the horizon at the two places, affecting the apparent position of the sunrise point at the summer solstice, and of the sunset point at the winter solstice.

Actually, it seems an extremely good agreement, considering the means of observation available in ancient times.

This coincidence is so close, therefore, that the conclusion is inescapable, that these two points on the distant horizon of Stonehenge were purposely established as landmarks, to indicate the solstitial turning points of the sun at the summer and winter solstices, as seen from Stonehenge.

Sir Flinders Petrie was at a great disadvantage in estimating the internal position of the axis of the Sarsen Circle, owing to the non-recognition of this important feature in the astronomy of Stonehenge, and in addition, by relying upon analogy, in assuming that the narrow space between the uprights of the standing trilithons, 12.8 and 12.4 inches, could be taken as a guide to the original space between the uprights of the great Central Trilithon, which he assumed to have been 13 inches.

This has been proved to be greatly in error, as will be seen later, by the exact measurements of the widths of these uprights, and of the length of the lintel stone, and the positions of the tenons and mortices, which unite to give a true measurement of the original space.  These measurements therefore show without doubt that this original space between the uprights of the great Central Trilithon was 3 feet instead of the 13 inches assumed by Sir Flinders Petrie.

Sir Flinders Petrie also accepted an average spacing of  36 inches between stones as being the probable space between Stone No. 16 and the fallen and displaced Stone No. 15 at the South-West end of the axis; which he thus gave as half the average space, 18 inches, from the side of No. 16.  He expressed some doubt about this distance, however, and said, “this is very vague.”

A more careful analysis of the width of the stones and their spacing, near this end of the axis, shows that Mr. E.H. Stone’s estimate of 5 feet 2 inches for the space between 15 and 16 is substantially correct, and that, like the North-East entrance, a wider than average space between the South-West stones was provided.

From the foregoing account, it is apparent that the true constructional axis of Stonehenge is not only definable from the internal structure of the monument alone, but also it coincides with the extensions to Grovely Castle in the South-West, and along the central line of the Avenue to the summit of Sidbury Hill in the North-East direction.

Petrie’s axis is affected by errors in both these respects, and it is clear that it is not the true axis.  It is therefore impossible to obtain from it a true astronomical date of construction.  Petrie’s axis points in a direction 50° 05’ 27” East of North, which was therefore, according to his measurement, the azimuth East of North of the point of midsummer sunrise when the Sarsen Circle was constructed.  This gives the solstitial declination of the sun, or what amounts to the same thing, the obliquity of the ecliptic at that date, namely 23° 38’ 11”.  We find then, from Newcomb’s formula, that the corresponding date is 471 A.D.  This date is quite unacceptable, in view of the archaeological results, as previously outlined.

But it has been shown in the foregoing astronomical investigations that Newcomb’s formula by itself does not give the true position of the sun in ancient times.   To get the true position of the sun, Newcomb’s formula needs a correction, supplied by the New Curve of the Obliquity of the Ecliptic, which corresponds with the ancient solar observations, and very strikingly, with the result obtained from the study of the great Solar Temple of Karnak, dating back to the year 2045 B.C.

We shall see presently that it also applies in the case of the Sarsen Circle of Stonehenge. 

Using this correction to Newcomb’s formula for the position of the sun corresponding to Petrie’s axis, we obtain in accordance with the New Curve, the date 764 A.D.  This is 293 years later than the date given by  Newcomb’s Formula, and is a quite impossible date for Stonehenge.  The source of error does not lie in the New Curve of Obliquity, but in the deviation of Petrie’s axis from the true direction of the ancient mid-summer sunrise as seen from Stonehenge.

It is to be pointed out that the New Curve always gives a later date than Newcomb’s Formula for any given value of the Obliquity of the Ecliptic, and this difference, which is very great in remote antiquity, decreases rapidly through the centuries, until it becomes zero at the end of the curve, viz. in 1850 A.D.

It can be seen, therefore, that for purposes of Chronology or Archaeology, when solar observations have been made at a Solstice, and a precise linkage with the sun’s position has been made, this astronomical method of dating provides a very sensitive criterion for verifying the true date of construction of such a building as the Stonehenge Circle, the Karnak Temple, or any other of similar kind.

We shall see presently, in the case of Lockyer’s axis, which is very near to the true one, the astronomical date from his observations, using Newcomb’s Formula, is 1822 B.C., but the New Curve, from the same observations, gives the date 282 B.C., i.e. a difference of 1540 years later by the New Curve than by Newcomb’s Formula.

With Stone’s axis, which is still nearer than Lockyer’s to the true one, the date obtained from Newcomb’s Formula is 1850 B.C., but from the New Curve it is 322 B.C., i.e. 1528 years later by the new Curve than by Newcomb’s Formula.

From all these considerations we see very clearly that Petrie’s axis is not the true axis of Stonehenge, and cannot give the correct astronomical date of its construction.

Lockyer’s Axis:  Sir Norman Lockyer, one of the greatest British astronomers of his time, was deeply interested in Stonehenge.  His well-known book Stonehenge and other British Stone Monuments Astronomically Considered, published in 1906 (second edition 1909), gives a full account of his very thorough and careful series of astronomical observations at Stonehenge in June 1901, as well as of a great deal of work, which he did in investigating other ancient British stone monuments having an astronomical character.

His results at Stonehenge were also published in the Proceedings of the Royal Society in 1901, vol. 69, pages 137-147.  Messrs. F.C. Penrose F.R.S. and Howard Payn were associated with him in the observations at Stonehenge.

He was at a disadvantage in that the “leaning” stone No. 56 of the great Central Trilithon was still in its leaning and somewhat displaced position, and this adversely affected the observations at that point, as it had done before in the case of Sir Flinders Petrie’s axis determination.  It was made erect, and restored to its true position later on in the same year, 1901.

Sir Norman recognized that the axis of Stonehenge must have originally passed centrally through the Central Trilithon, for he says

The axis passes very nearly centrally through an inter-columniation (so to call it) between the two uprights (i.e. No. 30 and 1) of the external circle, and between the uprights of the western-most trilithon as it originally stood.

Of this trilithon, the southernmost upright with the lintel stone fell in the year 1620, but the companion survived as the leaning stone, which formed a conspicuous and picturesque object for many years, but happily now restored to its original more dignified and safer condition of verticality.

The inclination of this stone, however, having taken place in the direction of the axis of the Avenue, and as the distance between it and its original companion is known both by the analogy of the two perfect trilithons and by the measure of the mortice holes on the lintel they formerly supported, we obtain by bisection the measure (viz. 11 inches) from its edge of a point in the continuation of the central axis of the Avenue and temple and which has now to be determined very accurately.

We see from this statement that Sir Norman Lockyer estimated the total width of the space between the two uprights of the Central Trilithon as 22 inches; but it will be shown later on that the true distance, from exact measurements, was 36 inches.  We see also that Sir Norman recognized that there was a continuity of the axis of the Sarsen Circle with that of the Avenue. 

In order to carry out his intention of determining this joint axis very accurately, he then set up a “6 inch Transit Theodolite by Cooke, with verniers reading to 20” in altitude and azimuth,” at a station “A” situated on what he believed to be the axis, and at a distance of 61 feet to the South-West of the centre of the Sarsen Circle.

This station “A” was therefore outside the Sarsen Circle, and about 10 feet beyond its outer south-west edge.  From the station “A” observations were made of the sun and the North Pole Star (Polaris); and the azimuths (angles East of North) of the principle points connected with the monument were determined.

The first thing was to measure the exact direction of the Central Line of the Avenue.  In his account of this he says

The banks which form the avenue have suffered much degradation.  It appears from Sir Richard Colt Hoare’s account that at the beginning of the last century they were distinguishable for a much greater distance than at present, but they are still discernible, especially on the northern side, for more than 1300 feet from the centre of the temple, and particularly the line of the bottom of the ditch from which the earth was taken to form the bank, and which runs parallel to it.

Measurements taken from this line assisted materially those taken from the crown of the bank itself.  With this help and by using the southern bank and ditch wherever it admitted of recognition, a fair estimate of the central line could be arrived at.

To verify this, two pegs were placed at points 140 feet apart along the line near the commencement of the avenue, and four others at distances averaging 100 feet apart nearer the further recognizable extremity, and their directions were measured with the theodolite, independently by two observers, the reference point being Salisbury Spire, of which the exact bearing from the centre of the temple had been kindly supplied by Colonel Johnston R.E., the Director-General of the Ordnance Survey.

The same was also measured locally by observations of the Sun and of Polaris, the mean of which differed by less than 20” from the Ordnance value.

The resulting observations gave for the axis of the Avenue nearest the commencement an azimuth of 49° 38’ 48”, and for that of the more distant part 49° 32’ 54”.

The mean of these two lines drawn from the central interval of the great trilithon already referred to, passes between two of the Sarsens of the exterior circle, which have an opening of about 4 feet, within a few inches of their middle point, the deviation being northwards.

This may be considered to prove the close coincidence of the original axis of the temple with the direction of the avenue.   This value of the azimuth, the mean of which is 49° 35’ 51”, is confirmed by the information, also supplied from the Ordnance Survey, that from the centre of the temple the bearing of the principle bench mark on the ancient fortified hill, about 8 miles distant, a well-known British encampment named Silbury or Sidbury, is 49° 34’ 18”, and that the same line continued through Stonehenge to the south-west strikes another ancient fortification, namely Grovely Castle, about 6 miles distant and at practically the same azimuth, viz. 49° 35’ 51”.

For the above reason 49° 34’ 18” has been adopted for the azimuth of the Avenue.

Sir Norman Lockyer also records the azimuths, or bearings East of North which he measured, of two important points, namely, the peak of the Friar’s Heel Stone, and the exact centre between the entrance stones 30 and 1.  These are as follows:

Highest point of the “Friar’s Heel” – N 50° 39’ 05” E
Middle of opening in North-East Trilithon (i.e. middle of opening between entrance stones 30 and 1) – N 49° 42’ 50”E

From these azimuths, and from the measured distances from Sir Norman’s observing station “A”, the exact distance of Lockyer’s axis from each of these points can be calculated, namely:

  • Distance of Lockyer’s axis at its nearest point North-West from the peak of “Friar’s Heel,” 6 feet 0 inches.
  • Distance of Lockyer’s axis North-West from centre Entrance opening between Stones 30 and 1 – 0 feet 3.26 inches (It is therefore 1 foot 8.74 inches from the Eastern side of Entrance Stone No. 30).

At the first of these points, the Friar’s Heel, we have 5 feet 9 inches for the corresponding distance of Stone’s exactly surveyed straight line, through the middle of the Avenue and continued through the Sarsen Circle, which constitutes Stone’s axis, to be described shortly.

At the second point, the North-East entrance to the Sarsen Circle, Stone’s axis passes exactly through the middle point between Stones 30 and 1.

The distance between Lockyer’s axis and Stone’s axis at these two points is therefore (1) 3.0 inches at the Friar’s Heel and (2) 3.26 inches at the North-East entrance of the Sarsen Circle.  In both cases, Lockyer’s axis lies to the North-West of Stone’s axis, i.e. to the left hand side looking outwards towards the Avenue and towards the mid-summer sunrise point over Sidbury Hill.

From these two axial differences, and the distance 206 feet, between the two points, other relationships between Lockyer’s axis and Stone’s axis can be calculated; and the exact distance of Lockyer’s axis from other fixed points can also be found.

Thus, we find:

  1. The angular difference between Lockyer’s axis and Stone’s axis is very small, namely, only 22” of arc.
  2. Lockyer’s axis points slightly further to the East of North than Stone’s axis, and the azimuth of Lockyer’s axis being 49° 34’ 18” East of North, while that of Stone’s axis is 49° 35’ 56” East of North.
  3. Lockyer’s axis crosses Stone’s axis at a point in the centre of the Avenue half a mile North-East of the centre of the Sarsen Circle.
  4. At the centre of the Sarsen Circle, Lockyer’s axis is 3.32 inches from Stone’s axis, and on its North-West side.
  5. At the great Central Trilithon, Lockyer’s axis is 3.36 inches on the North-West side of Stone’s axis.  At this point, Stone’s axis is 18 inches from the eastern side of the standing Trilithon upright No. 56, so that Lockyer’s axis is 14.64 inches from the side of No. 56.
  6. At the South-West end of the axis, between Stone No. 16 and its fallen, and displaced, companion, No. 15, Lockyer’s axis is 3.39 inches to the North-West of Stone’s axis.  Stone’s axis, according to his exact survey measurement, is at this point 31 inches from the eastern side of No. 16; consequently, Lockyer’s axis is 27.61 inches from the eastern side of No. 16.

From the foregoing analysis, it is clear that  Lockyer’s axis inside the Sarsen Circle is linked with fixed points of the Circle by the following measurements

a) 3.26 inches North-West from the middle point between the Entrance Stones 30 and 1.

b) 14.64 inches South-East from the South-East side of the great standing Trilithon Stone No. 56

c) 27.61 inches South-East from the South-East side of Stone No. 16

Norman Lockyer recognized that the central line of the Avenue was vitally linked with the axis of Stonehenge as a sighting device for the mid-summer sunrise, and was essentially a prolongation of the internal axis.  His axis is so very close to the true one that it is difficult to come to any other conclusion.

However, he was at a disadvantage in estimating the central line of the Avenue, because, as he says, the banks had “suffered much degradation.”  This explains, in part, the difference which he found in the  azimuths of the near and distant ends of the axis of the Avenue:  49° 38’ 48” and 49° 32’ 54” respectively.

But there is another factor of which he was not aware at the time.  In choosing the site of his Station “A,” which was on his axis line 10 feet beyond the Sarsen Circle to the South-West, from which he made his various azimuths and other astronomical observations, he was influenced by the distance of the axis, as he accepted it, from the Central Trilithon upright, No. 56, viz. 11 inches.  This introduced an error of practically 3 ½ inches, by which small amount he was away from the true axial line, to the North-West of it, at his observing station “A.”

A calculation of the effect of this displacement on the observed azimuths shows that, with the amended position of the observing station “A,” he would have obtained for the azimuth of the near end of the axis of the Avenue 49° 35’ 33”, instead of 49° 38’ 48”, i.e. a reduction of 3’ 15”; and for the distant end of the axis of the Avenue 49° 32’ 12” instead of 49° 32’ 54”.

The mean of these two amended values for Lockyer’s azimuths of the near and distant ends of the axis of the Avenue, namely, 49° 33’ 52”, is almost identical with that of Stone’s continuous straight line, representing the axis both of the Sarsen Circle and of the Centre line of the Avenue, 49° 33’ 54”.

It thus confirms the belief, expressed earlier in this chapter, and held by both Sir Norman Lockyer and Mr. E.H. Stone, that the centre line of the Avenue is the exact prolongation of the original axis of the Sarsen Circle, and was purposely designed by the builders of Stonehenge to point accurately to the position of the mid-summer sunrise over the summit of Sidbury Hill just as they saw it when they built the great Sarsen Circle.

Further, Sir Norman Lockyer and Mr. Stone both relied implicitly on the universally accepted belief of astronomers in the accuracy of the formulae used by them for giving the true position of the sun in ancient times.  For that reason, Sir Norman Lockyer, using Stockwell’s formula, obtained the astronomical date 1680 B.C. (with a possibility of error of 200 years, before or after that date, owing to the slow rate of change of the Obliquity of the Ecliptic), as the most probable date of the building of the Sarsen Circle; and Mr. Stone, using the same azimuth of the axis, 49° 34’ 18”, and the more recent formula given by Simon Newcomb, obtained the date 1840 B.C., with a possible error of 200 years either way, so that he says in his book (page 30) “as determined by astronomical considerations, the date for the building of the present structure of Stonehenge was probably not earlier than about 2040 B.C., and not later than about 1640 B.C.”

We see, from the results, that the astronomical date, found by using either Stockwell’s or Newcomb’s formula, is greatly out of agreement with the modern archaeological investigation previously described.  When the formula is corrected, however, by means of the New Curve of Obliquity, in the same way as for the oriented Solar Temple of Karnak, then the astronomical date agrees with archaeology and history.

The revised astronomical method therefore becomes a helpful one in problems of archaeology and chronology, when the essential solar observations are available.

For his solar observations at Stonehenge, Sir Norman Lockyer measured the altitude of horizon in the direction of the axis, and found it to be 35’  30”.  He assumed that the sunrise observation would correspond to the upper edge of the sun 2’, i.e. one-sixteenth of the sun’s diameter, and just visible above the horizon.  He adopted corrections for the combined refraction and solar parallax effects 0° 27’ 20”; and the sun’s semi-diameter 15’ 45”.  Using 49° 34’ 18” as found by the Ordnance Survey for the azimuth of the axis of Stonehenge, and thus also for the azimuth of the sun at midsummer sunrise at Stonehenge, and taking the latitude of Stonehenge as 51° 10’ 42” North, he then calculated the solstitial declination of the sun, and thus the Obliquity of the Ecliptic, 23° 54’ 30”, and hence the epoch of building the Sarsen Circle of Stonehenge 1680 B.C., as given above. 

In place of this, the New Curve gives the date corresponding to Newcomb’s axis 282 B.C., which is within 68 years of the probable historical and archaeological date, about 350 B.C.

A difference of 68 years, which is small, having regard to the nature of the problem, might be accounted for in several ways, such as (1) a small error in the assumed axis; (2) the edge of the rising sun observed slightly higher than the 2’ assumed by sir Norman Lockyer, say 4’ or 5’, which change would occur within 15 seconds from the  first moment of observation; (3) a difference in the height of the trees forming the distant horizon on the summit of Sidbury Hill, compared with those of today.

Cunnington’s Axis:  In his book, Stonehenge and its Date, published in 1935, Col R.H. Cunnington defined the axis of Stonehenge, which he calls “the central axis,” as follows:

Lockyer says that his axis passes through the centre of the Sarsen Circle, and within a few inches of the central point between the entrance stones 30 and 1; and by calculation from his data their exact distance is found to be 3 ½ inches as we look outwards.

The central axis, passing through both central points, differs therefore from Lockyer’s by 3 ½ inches in 50 feet, which is equivalent to 20’ in the angle.

Lockyer’s axis is 49° 34’, and from Newcomb’s Table of Obliquity the date would be 1840 B.C. (It has been corrected since Lockyer wrote, so that the date is a little different).  The difference of 20’ is equivalent to a difference of 1440 years, so the central axis brings the date to 400 B.C. (a still closer calculation gives this date as 366 B.C.)

From the above we see that Cunninton’s axis (1) coincides with Lockyer’s adopted centre of the monument, (2) passes centrally through the entrance stones, and (3) has an azimuth of approximately 49° 54’.   Lockyer’s centre was not directly linked with any fixed mark, but the date which he gives enables it to be ascertained with certainty.

We shall see later that Lockyer’s centre cannot be regarded as the true structural centre of the Sarsen Circle, but is displaced 3 1/3 inches to the westward.  We can, however, define Cunnington’s axis with reference to fixed marks by noting that, in addition to passing centrally between the entrance stones 30 and 1, it also passes the Friar’s Heel stone at a distance of 4 feet 7 inches west of the peak of the Heel Stone.

Also, the calculations show that Cunnington’s axis is 12.9 inches east from the Central Trilithon Stone No. 56, and 24 1/3 inches east from Stone No. 16.  Similarly it is found that the azimuth of Cunnington’s axis is 0° 19’ 15” greater than that of Lockyer’s axis, and is 49° 53’ 33” East of North, or, as Cunnington gives it, 49° 54’ to the nearest minute of arc.

When Cunnington’s axis is produced North-Eastward, it diverges considerably from the centre of the Avenue, and is displaced nearly 10 feet to the right of the central line of the Avenue at its distant end.  Cunnington was of the opinion “that the lines given by the Stones and the Avenue do slightly diverge.”

We shall see, however, that the correct estimation of the position of the centre of the Sarsen Circle and of the centre of the great Central Trilithon, brings the axis of the Sarsen Circle and the central line of the Avenue into exact agreement, so that there is no divergence between them.

Colonel Cunnington was completely satisfied that the builders of Stonehenge purposely gave it an orientation to mid-summer sunrise, for, as he says,

The Stones and Avenue are enough to prove beyond reasonable doubt that the monument is intentionally aligned on the midsummer sunrise, and most archaeologists are content to stop at that; but it is possible to go a good deal further; though on much less certain ground.

There is at least a possibility that the alignment was made very accurately and, if so, and if we could say exactly what it was, it might be possible to date the monument astronomically. 

There was a practical object that such an alignment could serve, and it is not always realized how important this may have been.

He then describes the probable use made of Stonehenge for correcting the ancient calendar, and continues,

It was only after Norman Lockyer took it in hand that this side of the matter was properly dealt with, and his book for a time made a considerable sensation.

Afterwards, however, the archaeological discoveries at Stonehenge showed that Lockyer’s astronomical date was seriously in error, and Colonel Cunnington comments that “Nowadays the whole subject of orientation has become distasteful to archaeologists; and this perhaps is why some prefer to think that Stonehenge has nothing to do with the Midsummer sunrise, and that its orientation is a figment of the imagination.”

Colonel Cunnington, however, was by no means of this opinion; but, using Lockyer’s assumed centre of the Sarsen Circle, and rectifying the axis to pass centrally through the space between the entrance stones 30 and 1, he thus found that with this new axis, and relying upon Newcomb’s formula to give the correct astronomical date, the date thus found agreed with his own well-based archaeological date.

It will now be shown that Cunnington’s axis is not the true structural axis of the Sarsen Circle, and cannot be the line originally pointing to the midsummer sunrise.  We thus see that Newcomb’s Formula only gives the right archaeological date when it is associated with a compensating error in the assumed axis.

Conversely, if the true structural axis is used, then, in order to get the right astronomical date of construction, Newcomb’s Formula itself must be corrected by a certain factor, and this is the factor given by the New Curve for the date in question.

It may be suggested here that an additional check upon the centre of the Sarsen Circle might be found by measurements based on the geometry of the “Four Stations,” previously described; and it seems reasonable to believe that such measurements would confirm the centre about to be described in connection with Stone’s axis. 

From the azimuth of Cunnington’s axis, 49° 53’ 33” East of North, the calculated solstitial declination of the Sun, or the Obliquity of the Ecliptic, is 23° 44’ 25”.  From this, with Newcomb’s formula, the corresponding astronomical date calculated for the building of Stonehenge is 366 B.C., as previously stated.  With the New Curve the date is 436 A.D.  This date is, of course, quite unacceptable, but, as in the case of Petrie’s axis, the fault does not lie in the New Curve, but in the error of the direction in which Cunnington’s axis points, 49° 53’ 33” East of North.

Instead of this, we shall now see that the Ordnance Survey azimuth, 49° 34’ 18” East of North, from the centre of the Sarsen Circle to the summit of Sidbury Hill, truly corresponds, as Sir Norman Lockyer realized, to the actual direction of midsummer sunrise, as seen from Stonehenge when the Sarsen Circle and the Avenue were constructed.

Stone’s Axis:  Mr. E.H. Stone, a member of the Institution of Civil Engineers, and of the American Society of Civil Engineers, made a careful survey, in June 1923, of the centre-line of the Avenue, and of its prolongation through the Sarsen Circle.  He described this work in his book The Stones of Stonehenge, published in 1924.  Mr. Stone defines the axis of Stonehenge as follows:

The Axis of the main structure of Stonehenge as erected by the builders is the line passing midway between stones 56 and 55 of the Central Trilithon, and midway between Stones 30 and 1 of the outer Circle.  It is obvious that the term “Axis of Stonehenge” would be meaningless as applied to any other line. (p. 131)

In an earlier part of his book, p. 20, he also indicates that we should expect to find the Axis passing midway between stones 15 and 16 of the outer circle.  Of this pair, No. 15 has fallen.  The broken upper part with its two tenons is still lying inside the circle. 

An analysis of the width of the Sarsen Stones and the intervening spaces will be given presently.  This shows that it is possible to make a close estimate of the original width of the space between 16 and 15, and that Stone’s axis, in all probability, does pass centrally through the original opening between these stones.

Mr. Stone’s survey of the Avenue and of the continuation of its centre line through the Monument is entitled to be regarded with confidence owing to his qualifications as an Engineer and Surveyor.  His statement of these results is as follows:

In June of 1923 some measurements on the Avenue were made by the author with a view to determine the direction of this centre line in relation to the Axis of Stonehenge.  These measurements were taken where the position of the banks and ditches is better defined than elsewhere – over a length of about 750 feet, extending from about 540 feet to about 1290 feet from the centre of the structure.

The actual ditches as originally excavated in the chalk are known to be V-shaped in section, and a  number of probings, with a steel bar, were taken by Colonel Hawley at intervals, by which successive positions of the bottom of the V for each ditch were approximately determined.  The points along the centre line of each ditch thus ascertained were plotted to a large scale, and it was found that, over a length of 750 feet on which the measurements were taken, the ditches are practically parallel and at a distance apart of about 71 feet centres. 

It was observed moreover that the centre line drawn between the two ditches, when produced, would pass just about midway between the Entrance Stones Nos. 1 and 30 of the Stonehenge Circle. (p. 126)

Mr. Stone considered that the results “warrant the conclusion that the centre line of the Avenue was intended to be a prolongation of the Axis of the structure.”

He therefore produced his “survey centre line.”  It passed

exactly mid-way between Stones 30 and 1 of the outer circle, and was  produced across the Stonehenge area and out to the other side of the circle beyond Stone No. 16.

This long straight survey centre line was marked on the ground, with pegs at intervals for convenient reference.  At the Central Trilithon it was found that this line passed just 18 inches to the right (south-east) of Stone No. 56.  The survey centre line thus occupies precisely the position determined independently as the probable line of the Axis.

This last remark refers to a careful measurement, made by Mr. Stone, of the lintel stone which originally stood on top of the central trilithon stones Nos. 56 and 55, and of the width of these stones, and an estimation of the width of the space between them.

Mr. Stone’s estimate was that the original space between Nos. 56 and 55 was “not less than 2 feet 6 inches, and not more than 3 feet 6 inches – the mean being 3 feet.”  We shall see presently that his estimate of an original 3 feet between the central trilithon stones 56 and 55 is exact, so that the Axis passed at a distance of 18 inches from the eastern side of the present standing Stone No. 56.

Mr. Stone’s long survey centre line was also found to pass at a distance of 31 inches from the eastern side of Sarsen Stone No. 16.  At the Friar’s Heel Stone it was 5 feet 9 inches to the west of the peak of the Heel Stone.

Stone’s Axis and the Great Central Trilithon

It is of importance now to examine carefully the available data about the original space between the uprights Nos. 56 and 55 of the Central Trilithon.  Stone No. 55 is lying on the ground broken in halves (i.e. prior to its restoration in 1958), with the upper half lying partly on the altar Stone, which it evidently pushed slant-wise out of position when it fell.  From measurements on Petrie’s plan, the Central Trilithon, in its fall, was slewed round about 6 to 8 degrees to the northward. 

The western upright, No. 56, did not fall far from the vertical position, but came to rest against the top of the blue stone, No. 68,  in front of it, at an angle of 17 to 20 degrees away from the vertical.

Stukeley’s drawing, in 1722, shows it leaning at an angle of 20 degrees, and by 1901, when it was restored, this had increased to 25 degrees, its heavy weight having forced the blue stone, No. 68 in front of it, into an inclined position.  Before 1901 the inclination of the “leaning stone” had been noticed for some years to be increasing to a dangerous angle. 

On the other hand, the eastern upright, No. 55, fell to the ground with such force that it was broken into two pieces.  It also fell obliquely towards its companion, No. 56.

The cause of this was evidently the strong foundation of No. 56, (which was sunk nearly 8 feet into the ground)  together with the coupling effect of the great lintel stone.  If the two uprights had been equally free to fall, they would have maintained their parallelism, and the original spacing between them would have been preserved.  But the constraint exercised on No. 55 by its firmer companion, aided by the connecting lintel stone, caused No. 55 to fall inward.  In doing so, it crashed heavily on the upper edge of blue stone No. 66, smashing it off, so that only the stump was left.  It also pushed the central blue stone, No. 67, obliquely over northwards, and uprooted it.

The retarding and pivoting effect of these two blue stones, added to the over-balancing weight of the lintel stone, forced the butt of no. 55 upwards out of the ground.  It also caused No. 55 to slip backwards four feet, and to topple over laterally towards No. 56.

This was particularly a consequence of the lintel coupling.  For, as No. 56 yielded much less to the disturbance, the lintel stone practically pivoted on the tenon of No. 56, and its other end traced out a curve which drew No. 55 over toward the north, by an amount which may be estimated geometrically as between 1 and 2 feet.

A model of the Central Trilithon, and of the blue stones 66, 67, and 68, in front of it, reproducing the conditions of its fall, demonstrates these effects clearly, and shows how the original space between the uprights was reduced in the fallen position.  This conclusion is confirmed by Mr. Stone’s measurement of the distance between the mortice sockets of the lintel stone, taking into consideration, also, the width of No. 55 and 56, and the position of the tenons.  The distance between the mortice socket holes was found by Mr. Stone to be 10 feet 6 inches from centre to centre.  The width of No. 56 was also carefully measured by him, and was found to be 7 feet 0 ½ inches just above the ground.  This stone is almost perfectly straight on its inner side till within less than a foot from the top, where the corner is slightly rounded off.

The bevel is on the outer side, so that the width of the upright diminishes from 7 feet near the ground to 6 feet near the top.  The tenon on the top of the stone is “not in the middle of the width of the stone, but is about 3 inches therefrom outwards.”  This is well seen on the photographs.  When a tracing is made of Petrie’s plan of the prostrate stone No. 55, and the two broken halves are fitted together, it can be seen that the inner edge of this stone, like No. 56, is also practically straight from about one foot from ground level to within four feet from the top, where there is a slight bevel, increasing to about 8 or 9 inches at the rounded corner.  On the outer side the top corner is broken off to a distance of four feet from the top, evidently where it struck the edge of the altar stone.  The part broken off would have included the tenon, which is missing.

The opening between the inner edges of stones 56 and 55 of the Central Trilithon from near ground level to within a few feet of the top was practically straight throughout, and its width may be estimated graphically, in accordance with the diagram shown as follows:

stoehenge reconstruction

Distance from centre of tenon of No. 56 to straight inner edge of 56  produced to top 3 feet, 3 inches
Distance of centre tenon of No. 55 (probable position) to straight inner edge of 55 produced to top 4 feet, 3 inches
7 feet, 6 inches
Distance between centre of mortice socket holes 10 feet, 6 inches
Difference = Width of opening of Central Trilithon 3 feet, 0 inches

The central blue stone, No. 67, now lying obliquely on the ground, is 3 feet wide, so that it just covered the width of the opening, and made a convenient arrangement for sighting on the point of mid-summer sunrise, from the point of view of an observer looking from the south-western side of the Monument.

The diagram shows the probable original dimensions of the Central Trilithon.  This confirms the accuracy of Mr. Stone’s survey centre line, passing centrally through the Trilithon, at a distance of 18 inches from the inner side of the upright No. 56.

Width of Opening Between Stones Nos. 16 and 15 of the Sarsen Circle

The probable width of this opening may be estimated as follows:

  • Stone No. 16 is still standing.  Stone No. 15 has partly disappeared, but the upper portion with the tenon is lying on the ground, and its width, measured on Petrie’s plan, is 6 feet 3 inches.
  • Stone No. 14 has fallen.  Its width near the original ground level is 5 feet 0 inches.
  • Stone No. 13 is missing.
  • Stone No. 12 is lying intact on the ground, and it was specially examined by Colonel Hawley in 1924.  He says

An excavation was made at the site of the fallen stone No. 12, and the area was extended later to include the missing stone No. 13.  No. 12 was found to lie over the hole it had stood in, and it had evidently slid back a little in falling.

The position of the stone made it difficult to work in the pit, but sufficient could be done to get a view of the interior.  It was sharply cut and had been shaped to take the stone without allowing any space at the sides.

The width of this stone, No. 12, is 6 feet 6 inches.  We can now obtain the probable width of the space between stones 16 and 15 as follows:

Width of Stone No. 15 6 feet, 3 inches
Width of Stone No. 14 5 feet. 0 inches
Assumed width of Stone No. 13
(see below)
6 feet, 5 inches
Total width of intervening stones Nos. 15, 14, 13 17 feet, 8 inches
Circular distance from near side of 16 to near side of 12, measured on Petrie’s plan at mid-point circle, corresponding to mid-thickness of stones 37 feet, 6 inches
Difference = total width of four intervening spaces 19 feet, 10 inches
Average width of the four spaces
4 feet, 11 ½ inches

This confirms, with a high degree of probability, the width of the space between Stones 16 and 15 at the south-western end of the axis found by Mr. Stone’s survey centre line, viz. 5 feet 2 inches; the survey centre line being half that distance, i.e. 31 inches from the South-East side of Stone No. 16.  It seems quite likely that the width of this space may have been slightly more than the others, and the adjustment made in a diminished width of Stone No. 13, which would then have been 6 feet 2 ½ inches, or 2 ½ inches less than the average width of the Sarsen Stones.

The following are the general widths of the Sarsen Stones at ground level, and of the spaces between them, which can be measured on Petrie’s plan:


Stone number
Width of Stone
Stone pair
Width of Space
6 feet 10 inches
30 - 1
4 feet 0 inches
7 feet 1 inch
1 - 2
2 feet 9 inches
6 feet 3 inches
2 --3
3 feet 6 inches
6 feet 1 inch
3 - 4
4 feet 3 inches
5 feet 3 inches
4 - 5
4 feet 1 inch
7 feet 6 inches
5 - 6
5 feet 4 inches
7 feet 1 inch
6 - 7
2 feet 11 inches
5 feet 3 inches
10 - 11
4 feet 1 inch
6 feet 8 inches
21 - 23
4 feet 9 inches
7 feet 8 inches
(see note below)
4 feet 9 inches
3 feet 7 inches
27 - 28
3 feet 0 inches
6 feet 7 inches
28 - 29
3 feet 2 inches
29 - 30
2 feet 9 inches
5 feet 0 inches
6 feet 3 inches
7 feet 5 inches
7 feet 9 inches
4 feet 5 icnes
6 feet 6 inches
6 feet 11 inches
6 feet 10 inches
6 feet 6 inches
7 feet 1 inch
7 feet 6 inches
6 feet 10 inches
8 feet 1 inch
Average width
6 feet 5 inches
Average space
3 feet 9.5 inches


NOTE: Two spaces, allowing for width of fallen and displaced Stone No. 22 (6 feet, 6 inches, as shown above in second column)

It will be seen that the width of the stones, and spaces between them are by no means uniform. Stone No. 11 was unusually narrow, and was not provided with a lintel stone, possibly, as has been suggested, to allow of a wider southern entrance for processions, with banners. The other stones vary from a maximum width of 8 feet 1 inch (No. 30) at the north-eastern entrance, to 4 feet 5 inches (No. 21).

Some of the stones have weathered more than others on account of varying degrees of hardness, but the majority of the stones are within 6 inches of average width. 

The same lack of uniformity is seen also in the spaces between the stones.

(Note: If we take 30 times the combined average width of the stones and of the spaces, we have for the total circumference of the circle, on which the inner faces of the stones are situated, 305 feet 0 inches.  The diameter of this circle is 97 feet 1 inch, which is in good agreement with Sir Flinders Petrie’s opinion, previously referred to, that the builders of Stonehenge intended the Sarsen Circle to have an inner diameter of 97 feet, so that the Circle itself would conform to the ancient standard “Year-Day Circle.”)

We see that the above considerations confirm both the accuracy of Mr. Stone’s measurements, and his claim that the Axis of the Monument and the centre line of the Avenue are in coincidence with one another.

As pointed out previously, in connection with Lockyer’s axis, if Sir Norman Lockyer had placed his observing station “A” only 3 ½ inches eastward of the position which he adopted, he would have obtained a much closer agreement between the azimuths of the near and distant ends of the Avenue.  He would then have found the amended mean value, 49° 33’ 58”, so close to the Ordnance Survey azimuth of the bench mark on the summit of Sidbury Hill, 49° 34’ 18”, differing from it by only 20”, so that he would have been convinced beyond doubt that the centre line of the Avenue was the exact prolongation of the Axis of Stonehenge, truly fulfilling the intention of the builders in this respect.

The Azimuth of Stone’s Axis, and the Corresponding Astronomical Date of Construction of the Sarsen Circle

In Mr. Stone’s book, the Stones of Stonehenge, printed in 1924, no independent determination of the azimuth of his axis of Stonehenge is given.  He accepted, for his own axis, the Ordnance Survey azimuth of the “Axis of Stonehenge” used by sir Norman Lockyer, viz. 49° 34’ 18”;  and, with a later value of Newcomb’s Formula, he obtained a date of construction about 1840 B.C. (Stone, p. 30). 

As given by Sir Norman Lockyer, the information supplied to him by the Ordnance Survey was that “from the centre of the temple the bearing of the principal bench mark on the ancient fortified hill about 8 miles distant, a well-known British encampment named Silbury or Sidbury, is 49° 34’ 18”.”

From Sir Norman Lockyer’s account of his proceedings at Stonehenge, it would appear that Colonel Johnston, R.E., the Director General of the Ordnance Survey, cooperated with Sir Norman in this matter, and no doubt sent a surveyor from the Ordnance Survey Department to make the necessary exact observations on the spot, making them from a central point chosen by Sir Norman Lockyer as the most probable centre of the Sarsen Circle, as well as he could ascertain it.

It has already been pointed out that, owing to the elevation of the intervening down-land, the principal  bench mark, which represents the highest point on Sidbury Hill (or perhaps it would be better to say the approximate centre of the area forming the summit of the hill), is not easily discernible from Stonehenge.

This difficulty, however, would of course be simply overcome in such a survey observation by using a high measuring staff on the site of the bench mark.  On the line thus surveyed, and continued backwards beyond the South-West part of the Sarsen Circle, Sir Norman Lockyer fixed his observing station “A” which, he states, was on his axis line, “at a distance of 61 feet to the South-West of the centre of the temple,” and from which he made observations of the sun and of the North Pole Star, Polaris, and in addition determined the azimuth of principle points connected with the monument.

As he says, “This axis line passed very nearly centrally through an inter-columniation (so to call it) between two uprights of the external circle,” i.e., between the entrance stones 30 and 1.  It was not, however, exactly central between them, and, as we have already seen, an exact calculation shows that it was 3.26 inches to the west of the centre of the entrance.

This difference, small though it is, shows that, as Colonel Cunnington pointed out, Sir Norman Lockyer’s axis cannot be the true structural axis of the monument; and it is due to Mr. Stone, by his excellent survey, that the true structural axis was precisely located, and the true structural centre of the Sarsen Circle must therefore necessarily have been on this axis.

It should further be indicated here, however, that although Sir Norman Lockyer’s assumed centre of the Sarsen Circle was only a very small distance (3.32 inches) west of the true centre of this Circle, this displacement, in the long distance of 8 miles to the bench mark on Sidbury Hill, would only give rise to a very small difference, viz. 1.5 inches in the observed azimuth of the bench mark. 

Thus, if the observation of the bench mark on Sidbury Hill had been made from Stone’s constructional centre of the Sarsen Circle, 3.32 inches East of Lockyer’s centre,  then the azimuth of the bench mark would have been 49° 34’ 16.5” instead of 49° 34’ 18”, found by the Ordnance Survey from Lockyer’s centre.  this difference is so small that it is practically negligible, as it would only alter the calculated date of construction of the monument by about three years.

But we must now notice that the measurements of the bench mark as the distant extremity of the Stonehenge axis involves the assumption that this particular spot on the summit of Sidbury Hill was the exact point of midsummer sunrise at the date of the construction of the Sarsen Circle.

The structural axis of Stonehenge, accurately established by Mr. Stone from his measurements within the Circle itself, and continued in a single straight line along the centre of the Avenue to the distance of 1290 feet from the centre of the monument (Stone, p. 126), involves no assumption regarding the bench mark on Sidbury Hill.  It was clearly the line intended by the builders of Stonehenge to indicate by its prolongation the point of midsummer sunrise as they saw it at the date of the construction of the Sarsen Circle.

We must therefore find the azimuth of this line, and although it is not given in Mr. Stone’s report, it can be easily calculated from the data which he gives, combined with the azimuth of necessary points measured by Sir Norman Lockyer.  Thus, Sir Norman Lockyer gives the azimuth of the exact centre between the Entrance Stones 30 and 1, and measured from his observing station “A,” viz. 49° 42’ 50”.

This observing station was 3.40 inches west of Stone’s axis and was at a distance of 109 feet 6 inches, or 1314 inches altogether, from the inner face of the entrance stones 30 and 1.  This corresponds to an angle of 0° 8’ 54”, to be subtracted from Sir Norman Lockyer’s measurement, 49° 42’ 50”.  the result gives us 49° 33’ 56" as the azimuth, or bearing East of North, of Stone’s axis.

Further, it is shown by calculation that Lockyer’s axis intersects Stone’s axis at a point in the centre of the Avenue, 2377 feet distant from the centre of the Sarsen Circle.  The angular difference between Lockyer’s axis and Stone’s axis (49° 34’ 18” –  49° 33’ 56”)  is 0° 0’ 22”.

Stone’s axis is directed towards a point on the horizon a little farther to the West than Lockyer’s axis.  From the point of intersection of the two axes there is a distance of approximately 7 miles 2803 feet, and at this distance the angular difference of 0° 0’ 22” corresponds to a difference of 4 feet 3 inches.

Since Lockyer’s axis is directed towards the bench mark on Sidbury Hill, we thus find that the extremity of Stone’s axis is at a point 4 feet 3 inches west of the bench mark.  The difference is comparatively small, and the angular difference to which it corresponds, 0° 0’ 22”, represents a difference in the date of construction, astronomically determined with the new curve and tables of Obliquity, of 40 years, namely from 282 B.C. (Lockyer’s axis) to 322 B.C. (Stone’s axis). 

We also see that whereas Newcomb’s Formula gives a completely inadmissible date, 1822 B.C., for Lockyer’s axis, and 1850 B.C. for Stone’s axis, the New Curve, correcting Newcomb’s Formula by a hitherto unrecognized factor, gives an astronomical date for Stone’s axis 322 B.C., which is in good agreement with the latest archaeology of Stonehenge, and is only 28 years later than the probably historical date of the reconstruction of Stonehenge by the famous King Belinus about the year 350 B.C.

stonehenge axes

The Stonehenge Trilithons as a Sighting Device for Observing the Summer Solstitial Sunrise

As pointed out by Colonel Cunnington in Stonehenge and its Date, p. 57, the height above ground level of the central blue stone, No. 67, of the blue stone horseshoe formation, was probably 8 feet, the full length of the stone being 12 feet; and this would prevent an observer, standing behind the Central Trilithon, from seeing the point of mid-summer sunrise on the horizon, unless he stood on some kind of platform.

But, as the ground slopes upward toward the South-West at an angle of about 1 ½ degrees, or 2.6 feet in 100 feet, an observer standing on the axis line at the inner edge of the bank, about 150 feet South-West from the centre of the monument, would have a unique view of the point of sunrise through the Sarsen Stone apertures 16-15, the Central Trilithon, and 30-1.  (Fig. 33)

From this point inside the enclosure, and on the inner edge of the bank, the angular field of view through the South-West Stones 16-15 would be 2°  54’.  This would be reduced at the Central Trilithon to 1° 22’, and further reduced, at the entrance stones 30 – 1, to 1° 11’.  From this point of view, the general arrangement of the Sarsen Stones 16 – 15 and 30 – 1, and of the Central Trilithon, with the central blue stone No. 67 in front of it, and with the rising edge of the mid-summer sun central in the picture, would have appeared as represented in the diagram above.


This unique rectangular framework, formed by the Great Sarsen Stones and the Central Trilithon, was admirably suited for the visual observation of the sun, and would no doubt have been made use of by the ancient astronomers responsible for the Celtic calendar, and would have been of special interest, just as today, when many people congregate at Stonehenge in order to witness, from a suitable position on the altar stone, the mid-summer sun rising, not, as formerly, in the central line of the axis along the centre  of the Avenue and over the summit of Sidbury Hill, but now over the top of the Friar’s Heel Stone.

With the arrangement available in ancient times, the observer then could not only make an accurate observation of the sun in its central position at sunrise on mid-summer’s day, but could also note its gradual approach to, and departure from, the solstitial turning point, during about ten days before and after the solstice, and thus could fix with accuracy the date and time of the summer solstice from year to year, just as the ancient astronomers of other nations, notably the ancient Chinese, also did in their system of astronomy.

In addition to this method of observation at Stonehenge, it seems likely that the turning points of the sun, at midsummer sunrise and midwinter sunset were also marked by the construction, at the same time as the building of Stonehenge, of the two special landmarks on the horizon, viz. the Sidbury Hill fortification in the North-East and the corresponding one at Grovely in the South-West, which are both considered to be Early Iron Age.

Anyone who has consistently watched the daily movement of the sun, at the sunrise or sunset points throughout the year, can appreciate the interest and advantage  of either natural or constructed landmarks, to indicate the position occupied by the sun at important dates of the solar year.  It therefore seems probable that the unique alignment illustrated was intentionally provided by the builders of Stonehenge for this astronomical purpose.

The Friar’s Heel Stone

Much speculation has been made concerning the astronomical purpose of the friar’s Heel Stone, in connection with the midsummer sunrise.  On account of the downward slope of the ground from the centre of the monument towards the Heel Stone, and beyond it, at an angle of about 1 ½ degrees from the horizontal, or about 2 ½ feet in 100 feet, the peak of the Heel Stone can be seen level with the distant horizon, and at an altitude of 0° 35’ 30”, by an observer standing on the Altar Stone.

It has been supposed that perhaps the sun was seen from this position, with its lower limb apparently just touching the peak of the Heel Stone, when it had risen sufficiently high to bring it into the correct azimuth, approximately 50° 48’ East of North, as seen from the centre of the Altar Stone.

This is not so, however, as the altitude of the sun’s lower limb, with the effect of refraction and parallax included, would have been 0° 49’ 30”; that is, the whole of the sun’s disc would be clear of the peak of the Heel Stone by an amount of 14’, or nearly half of the sun’s diameter.

It was suggested by E. Duke, however, in his book Druidic Temples, p. 133, published in 1846, that the Friar’s Heel Stone was “a gnomon for the purpose of observing the rising of the Sun on the auspicious morn of the summer solstice.”

Edward Barclay, in his book Stonehenge, 1895, p. 11, also refers to it as an “’Index Stone’…by means of this large unwrought rock, the temple is set to the rising sun at the summer solstice.”

To examine these statements, we must now ascertain where the edge of the shadow cast by the heel Stone would have fallen when the sun was in line with the Heel Stone, as seen from the centre of the Altar Stone.  Calculation of this shows that, at the time of building the Sarsen Circle, about 350 B.C. according to the preceding results, the apparent altitude in the sky of the upper limb of the sun (the sun’s declination then being 23° 54’ 41” N.) when it reached the azimuth of the Friar’s Heel Stone, as seen from the Altar Stone, would have been 1° 20’, including the effect of atmospheric refraction and solar parallax.

This solar altitude, however, must be reduced by 3’ to 1° 17’, for shadow observations, since the edge of the dense shadow cast by the Heel Stone would correspond to 3’ of the upper edge of the sun being above the top of the Heel Stone, as seen from a point at the shadow’s edge.

The geometry of a vertical section of Stonehenge shows that the horizontal plane, on which this shadow edge would fall, in the vicinity of the Altar Stone, would be 2 feet above the surface level of the Altar Stone.  the actual shadow of the peak of the Friar’s Heel Stone would therefore fall upon the central blue stone, No. 67, which stood right in front of the great Central Trilithon.

The varying height of this shadow, and its movement, as seen on the central blue stone in the early mornings, at and near the date of the summer solstice, would thus justify the opinion of the Rev. Edward Duke that the Friar’s Heel Stone, the “stone of the rising sun,” “was a gnomon for the purpose of observing the rising of the sun on the auspicious morn of the summer solstice.”

Summary of the Evidence Relating to the Date of Building Stonehenge

The foregoing evidence, derived from the astronomy and the archaeology of Stonehenge, confirms the belief

  • first, that the reconstruction of this great British monument of antiquity was affected in Celtic times, when the Celtic religion, or Druidism, had reached a high degree of supremacy in Britain, and probably about the year 350 B.C.;
  • secondly, that the Sarsen Circle and other important features, especially the long straight  entrance Avenue, were intentionally oriented by the builders of Stonehenge with the greatest care and precision towards the point of mid-summer sunrise over the summit of Sidbury Hill;
  • third, that these conditions, and this date, cannot be harmonized with the position of the sun as given by Newcomb’s Formula for the Obliquity of the Ecliptic in those ancient times.

On this account, it has become the common opinion amongst archaeologists that astronomical orientation cannot be relied upon to throw any light on the true date of construction of Stonehenge.

On the contrary, however, the New Curve of the Obliquity gives the necessary factor of correction to Newcomb’s Formula, enabling the true position of the sun in ancient times to be ascertained, and it thus gives an astronomical date for Stonehenge very close to that which is indicated by history and by modern archaeology.

Therefore, just as in the case of the Solar Temple at Karnak, the conclusion is obtained that the great British monument of Stonehenge confirms, in an unique and remarkable way, the accuracy of the New Curve of the Obliquity of the Ecliptic, which includes not only the normal curve of the age-long movement of the earth’s axis expressed by Newcomb’s Formula, but also the curve of recovery of the axis after its displacement in the year 2345 B.C., as indicated by the examination of the ancient, mediaeval, and later astronomical observations discussed in the earlier chapters of this book.



continue to Chapter 10