Stonehenge: Neolithic Man and the Cosmos

The long barrow off Beckhampton Road lies less than 4 km west of that at West Kennet. As mentioned earlier, it is one of an important trio excavated between 1959 and 1967—in this case in 1964 under the direction of I. F. Smith. It was described by William Stukeley in 1743 as ‘pyriform’ (pear-shaped), and ‘longish, but broad at one end’. It had been over 50 m long, and was originally flanked by splayed ditches, with its broad end roughly northeast. That end had been transformed when a round barrow was superimposed on it, millennia before nineteenth-century farmers levelled and ploughed the whole thing. In that same century it was dug into by archaeologists too. One of them, John Thurnam, recruited his labour from among his patients at the Wiltshire County Asylum in Devizes. Despite all of this activity, the ground beneath the barrow retained a few secrets of immense interest, to be recovered in the modern excavations.

Especially important were signs of the care with which directional properties had been assigned to the barrow. A row of stake holes was found to run along the axis, changing direction abruptly in a middle section, before returning to the original direction. Offset from this bent axis were traces of further straight rows of stake holes, making for at least twenty bays at the wider end. The staking out of some of the bays on the northern side, where the round barrow had been superimposed, and probably that of others at the narrower end, have been lost. Other rows of stake holes mark the edges of the mound, and those to the southeast side make an extremely well-defined line. Some rows were pushed out of true by the weight of soil, although much care had obviously gone into establishing them in the first place. Generally speaking, stake holes had a depth of from 15 to 60 cm, and the stakes, of diameters up to about 8 cm, had been pointed, so they must have been hammered into the ground. Much the same procedures were followed at the South Street barrow.

In Fig. 35 (#ulink_8e2cd48f-8c9a-5b1b-839e-2bfcf84d9ee0), the better-defined rows of stake holes have been indicated, that is, when they are of reasonable length and have clearly not suffered distortion through soil pressure. (To see the individual holes, the original report will have to be consulted.) The excavation brought to light even more valuable structural evidence than this, in the form of hollow casts representing rods and poles that had been used in various ways and had later rotted. Traces of poles were found to the side of each row. They had clearly been tied in some way to the uprights, certainly not to hold back the material of the mound, but surely to fix a straight line. The line was important because it was what settled the precise form of the barrow, and on the assumptions made here that form was intimately related to a line of sight. From signs of accidental spillage of material during the construction it was clear to the excavators that the bays, or opposite pairs of bays, were built one at a time.

Bays such as those at Beckhampton Road are reminiscent of others in barrows at Sarnowo (Poland), Skendleby (Lincolnshire), Ascott-under-Wychwood (Oxfordshire), and the neighbouring South Street barrow. Paul Ashbee has noted, furthermore, that various Cotswold long barrows dug into in the nineteenth century were found to be split axially and into bays with stones, and that stake holes might there have been missed. The Beckhampton Road barrow is an important guide to the meaning of these bays, and it is no exaggeration to describe them as an astronomical plan, analogous to the scaling posts of the barrows at Fussell’s Lodge and Wayland’s Smithy.

The stake holes constituting the bent axis of the barrow begin and end (rr) at two almost perfectly identical azimuths, paralleled at the northeastern end by the bounding rows p and t. The accuracy with which these are laid out is noteworthy: averaged over their lengths, the mean azimuth is 49.8°. It gives great satisfaction to find that the transverse lines of stake holes turn out to be perpendicular to one side or the other, for this is exactly what our principle of perpendicular viewing at equal altitudes leads us to expect. As explained earlier in this chapter, however, it is chastening to find that the b-rows are at right angles to features on the opposite edge of the mound, judging by row q to the distant side. There can be no doubt that viewing was along the lines of the b-rows from the southeastern ditch (sector EG at the very least), and that viewing was along the lines of rows a looking southeast from ditch sector AB and perhaps BC. The mound edges seem to be perversely arranged, but they matter less than the ridges. The a-rows are well suited to row r, but not to row q, and the b-rows to row q (where they are not to be found) but not to row r.

FIG. 35. The overall structure of the Beckhampton Road long barrow, as indicated by the ditches, the approximate edges of the mound (coarse broken lines) and selected rows of stake holes (continuous lines within the mound). A few individual stake holes are marked at the northeast. These are joined by broken lines (x and y). Note the precision with which they cross on the axis, and note also the merest hint of a scaling-post construction near the letter x. Where transverse stake hole rows are close to parallel, they are labelled with the same letter: there are only three clear groups. Judging by consistency alone, the estimated edges of the ditch and the mound are plainly less reliable as astronomical indicators than the stake hole rows. The ditches are divided into sectors (see letters A to K) according to supposed astronomical function. Ox skulls were found at the points marked.

Does this not fit uncomfortably with the principle of perpendicular viewing? Not at all. The axial rows cannot be taken as a simple ridge line. The supposed lines of sight would have been tangential to the mound below the ridge, unless the spine came to a sharp edge. Any axial ridge would not have been strictly seen, and would have been slightly flattened, if only by weathering, so that the effective ridge would have been double. The angle of view on this occasion was almost certainly about 15.3°. The reasoning follows the principles laid down earlier. Starting from the azimuths of a and b (both derived with the help of longer rows t and s but not the less reliable edge of a turves line e), stars at equal altitudes are sought. Ditch depths are compatible with this idea, although further excavation of them would not come amiss. From azimuths 135.8° and 309.8° and a latitude of 51° 24’ 28", it seems that the setting of Deneb was observed to the northwest and the rising of Bellatrix to the southeast. A strict application of previous principles, overlooking imperfections in their implementation, provides a common altitude 15.32° and a year of 3320 BC. There are many imponderables here, but the date is probably accurate to better than a century. (The altitude is finely tuned, since Deneb’s declination changes so slowly, and no other bright star offers itself.) As for the date, it is perhaps not without significance that the mid-section of the barrow (row q) aligned accurately on the setting of Rigel around 3320 BC, over the natural horizon.

Stukeley’s ‘pyriform’ barrow was so only because it had been deformed by the later addition of a round barrow to the wider end. It is clear that it originally had a trapezoidal form, and since the ditches extend so far to the southwest, we must suppose that the barrow ended in the neighbourhood of Z (Fig. 35 (#ulink_8e2cd48f-8c9a-5b1b-839e-2bfcf84d9ee0)). The directions of lines x and y were clearly those of a chevron-shaped façade. How this was used is less clear, but over natural ground, Pollux set in the direction of x (around 3360 BC) and beta Centauri rose in the direction of y in 3380 BC—or say a century earlier with a cover of seven-metre trees.

The lines of x and y meet almost precisely on the axis, at a point well fitted, therefore, for a triple observation, if only there were something to be seen along this part of the main axis. There was indeed something to be seen: the last glint of the setting midwinter Sun (that is, at the solstice) was along this line. Precise dating is impossible, but taking the azimuth as 226.2° (it differs from that of the westernmost part of the axis by half a degree) and the altitude of the horizon set by a treeless valley floor as 2.3°, the direction is virtually perfect for the period in question. Viewing could have been along the ridge itself, given a platform on which to stand, but it would have been easier to look along the edges p and t. Long barrows may bend, but never, as far as can be seen, in such a way as to block views along their edges at the head of the barrow.

This is a highly significant finding—the first Wessex long barrow considered here that clearly incorporated an alignment on the Sun, although there must surely be many more, since six or seven centuries earlier a Lincolnshire long barrow (Skendleby 2) had done the same, and a square, overtly humble, but cleverly designed barrow at Grendon in Northamptonshire had done so too, say a century before South Street. (They will be discussed later in this chapter.) Sirius and important stars in Orion were within a degree of aligning, but not to the standards of accuracy found previously. The alignments of later circular monuments were almost invariably on the Sun and Moon, and it seems probable that the Beckhampton Road long barrow was colonized by the builders of the round barrow at its head precisely because it aligned on midwinter sunset.

Three ox skulls were found more or less in the line of the ridge, which again gave rise to speculation that the ox heads, perhaps with skins and hooves attached, had been set up on posts penetrating the back of the barrow. There is no sign of Aldebaran here, but as it happens there is an independent case to be made out for a switch of bull symbolism to midwinter sunset.

The main disadvantage of the scaling posts of the old structures at Wayland’s Smithy and Fussell’s Lodge was that they required a transference of levels, not very difficult when structures were of wood, but more so with earthen mounds. In some way or another, a horizon had to be built up until it produced the desired effect—but strictly in accordance with the requirements of right-angled viewing. There would have been only minor difficulties with the progressive shaping of the artificial horizon, as the bays were filled in, one by one, until at last rising and setting were seen in the required directions. The main intellectual problem was quite different: it was that of settling the directions. To reconstruct the method it is necessary to make a conjecture as to the starting point. There is a strong sense in which Beckhampton Road is a Rigel barrow. Rigel is the brightest of the stars concerned, and the alignment on it belongs to the site in the pre-barrow period. Assuming, then, that this was the star from which the builders began, here is a potential procedure:

Some method or other is needed to establish the positions of a pair of ridge poles at equal heights and at right angles to the lines of view to opposed stars, northern and southern in this case. Once they were established, ditches could be marked out, if not extensively dug at this stage, with appropriate sections parallel to the ridge-poles. There was still a degree of freedom left to the architects, who would have tried to accommodate other stars in their length-wise barrow lines. The central portion of the line of stakes will be assumed to align on the setting of Rigel, and the other pair on Deneb and Bellatrix:

(1) The stake holes XX were arranged to be in line with Rigel’s setting.

(2) Fences of stakes, to which poles were tied as cross-pieces, were set at right angles to that first line, and a viewing ditch cut parallel to it, for sighting on Bellatrix. Horizontal poles were raised along the ridge line until the star rises at that level and in the direction set by the transverse stakes. Hides could have been draped over them to give an obscuring horizon. The lengths of such poles would have been between 1.5 m and 3 m, and their weight offers no problem. Infilling of ditch material to make a solid horizon might have begun at this stage—in slices almost the reverse of an archaeological dig.

(3) A provisional ditch was started for viewing Deneb. (Approximate positions were of course known all along.) Another ridge-pole, at precisely the same level, was varied in its orientation until Deneb was seen to set precisely at right angles to it. Fences of stakes at right angles to the Deneb ridge-pole could then have been set up to confirm the arrangement, with viewing directions again made more easily visible by poles tied along them. This established perhaps all remaining directions.

(4) Ditches could next have been completed and the fences largely filled in. An arch of spaced parallel poles, like stringers in the body of an aircraft, could have been tied to the rows of stakes, to define the barrow’s form, although the removal of the stakes from one section might have been thought necessary before an adjacent section was added. The curve of the arch might have been fixed by templates, curved perhaps like longbows, with tow. The builders’ job was to fill up the arch with the materials of the mound, and to dress it smooth in a suitable way—with marl, chalk gravel, and turves. Section by section the barrow was so assembled, its wedge-like shape guaranteed by the lines of the ditches.

FIG. 36. The overall plan of the South Street barrow. The three most important sections are combined into one, for convenience, at the right. They correspond to the broken lines A, B, and C on the plan. Lines of sight to the eyes of observers in possible viewing positions, at approximately the correct calculated angle, are shown on those sections—which are, however, not perfectly chosen for our present purposes. The diagonal line of stakes (D) crosses the entire barrow. The larger sarsens are marked on the plan (notably S), in their present positions. On section B, however, sarsen S is placed upright, as it might at one time have stood, even before the barrow.

Assuming angles derived from the same sort of astronomical analysis as used for earlier barrows, now for the setting Deneb in one direction and the rising Bellatrix in the other, the resulting profile of the barrow conforms closely with I. F. Smith’s estimates of the shape the barrow originally had. Pollen analysis showed that the barrow had been built in an area of grassland, but with arable and wooded areas nearby. This barrow was not on high ground, and the best of all possible motives for the relatively steep angles of view of those who looked across the barrow from the ditches was to observe the stars well clear of nearby trees—in this case 15 m trees further away than 75 m would have presented no problem except in the line of the barrow—that lay along an arable valley floor.

South Street (#ulink_55f03d01-2ada-5bca-a2a6-e0ccafc8c4f9)

The last of the important trio of long barrows in this district is that off South Street in the parish of Avebury. It was erected in an area of arable land that had been cleared in the early fourth millennium BC. The surrounding country, predominantly woodland, contained hawthorn, oak, birch, elm, alder, pine, and other species, with all-pervasive hazel scrub invading the open pasture from time to time. It will be shown that this barrow was always extremely humble in outward appearance and material structure, and as an artificial horizon set rather low altitudes, but that it was high enough for sight-lines to clear nearby scrub and woodland. William Stukeley, in his book Abury (1743), described it as ‘broad and flat, as if sunk into the ground with age’; but broad and flat it had always been. Humble though it appeared, it embodied a most beautiful astronomical symmetry, and one that leaves us in no doubt that the people of Wessex were still actively developing their art.

The barrow was excavated under the direction of J. G. Evans in 1966–7. The road—South Street—runs across a corner of it, and the site has been much ravaged by time, not to mention proximity to the village. There are two large standing stones 120 m to the west of it, known as the Longstones, or Adam and Eve, but these belong to a much later period, as will be shown in connection with the Avebury avenues. Although there are no great quantities of stone in any of the three Avebury barrows, here at South Street there are several large and small sarsens at its principal end, and the larger stones were evidently set in place before the main construction, since all lines of stake holes curve round them where necessary. This barrow repeats in several respects the structure at Beckhampton Road, revealing a similarly straight row of stake holes defining an axis, and indeed more complete transverse rows than at that other barrow. The South Street barrow was divided by them into about 20 bays to each side of the axis. Again they were occasionally deformed in places by pressure of the mound, and again there were numerous traces of collapsed rods that had originally been fixed to them. There is a pair of ditches, uninterrupted in the South Street case, and splayed but not very markedly so. A simplified plan of the site as a whole is shown in Fig. 36 (#ulink_f09d63c8-5b0a-52e8-876f-f428daed1fb9), where rows of stake holes are represented by continuous lines (marking the axis and bays). Once again, those who dislike the element of approximation in all this may consult the original publication for the many hundreds of holes.

Applying the principle of viewing at equal altitudes, it is found that looking across the ditches, along the directions set by the bay-fences, Vega was observed rising in the northeast, and that Sirius was seen setting at an altitude of about 9° to the southwest. The date was in the neighbourhood of 3260 BC. A date seven centuries earlier, with Arcturus and Bellatrix, is rejected because it makes for an improbably high barrow, in fact over 5 m along the spine. The radiocarbon dates also speak against that solution.

This very general conclusion has to be qualified in several respects, since the large number of paired lines of stake holes means a large number of solutions, and not all are superficially in agreement. As Fig. 36 (#ulink_f09d63c8-5b0a-52e8-876f-f428daed1fb9) shows, these lines are by no means constant in direction, but it would of course be mistaken to take averages of azimuths, north and south. While—on our basic assumption—opposed altitudes are ideally equal, it need not be supposed that they were constant along the whole length of the ditches. Until the ditches are fully excavated we shall remain ignorant of the pattern of altitudes, but even now it can be said categorically that (1) the known ditches were almost perfectly equal in depth (in relation to the Ordnance Datum rather than surface levels) at the eastern end; and that (2) the ditch floor was somewhat lower there than in the neighbourhood of the point at which the compass rose is placed on Fig. 36 (#ulink_f09d63c8-5b0a-52e8-876f-f428daed1fb9). This second fact, that might at first sight seem to refute our basic principles, will on the contrary eventually serve to vindicate them.

From a naïve application of the principle of equal-altitude viewing, ten of the twenty pairs of stake hole rows are found to be usable to yield ten corresponding dates (and altitudes). The graphs giving a result for the first bay (actually based on the second pair of fences) are shown on the right-hand side of Fig. 37 (#ulink_214fe82f-7a44-585c-8d39-9f79cfb9209d). The date derived is 3260 BC and the altitude 9.42°. Until such time as further information on the ditches becomes available, this result will be the most reliable of the ten, since the corresponding observers are known to have stood at equal depths. Performing the same calculation for all ten of the straightest pairs of rows of stake holes, one finds a mean result of 3220 BC, but this is certainly less reliable than the first result, since it is known that not all corresponding points in the ditches further west are at exactly equal levels.

FIG. 37. The dating of the South Street barrow. On the right, the graphs for the setting of Sirius as seen in line with the first bay from the north ditch and the rising of Vega as seen similarly from the south, meet opposite the year 3260 and altitude 9.42°. On the left is the evidence for the sighting of Regulus and Bellatrix along the line of the diagonal row of stake posts at about the same time, but now at altitudes differing by about 0.92°. On the case of Capella, see the text.

The date of 3260 BC, probably good to within half a century, fits well with two out of four radiocarbon dates obtained from the site. The four, briefly, are these: from oak under the mound (2810 ± 130 bc, equivalent to 3535 ± 165 BC); from an ox vertebra (2750 ± 135 bc, 3495 ± 150 BC); from a red deer antler, north ditch (2670 ± 140 bc, 3360 ± 260 BC); from another, second bay of the mound (2580 ± 110 bc, 3190 ± 150 BC).

Without a knowledge of precisely where the observer stood, it is impossible to give a precise height for the barrow at the eastern end, but it was very close indeed to the height of a man’s eye above the carefully levelled ground on which the mound was erected (see sections at the right hand side of Fig. 36 (#ulink_f09d63c8-5b0a-52e8-876f-f428daed1fb9)). This means that it was just possible to look over the barrow from its façade, for instance, in ways that might have been indulged in before the barrow was built.

The calculated height in question is so close to the length of the sarsen marked S on the figure that it is tempting to suppose that it originally stood upright. It needed no significant stone hole, since it would have been held up by the chalk of the mound. This was not the opinion of the excavator, J. G. Evans, however, who noted that the mound material gave no evidence of collapse. He noted too that the three largest had been prepared for the positions in which they were found by having a slice of stone removed. We might have been inclined to see in S not a sighting stone but a stone that was meant to remain only just covered by the mound. Oddly enough, although it is too low for the mound in its prone position, it could have served this very purpose at an earlier stage, when a still lower angle had to be set by the mound. (This lower angle will be discussed later.) Attrition of such carefully prepared mounds by rain, wind, and invading plants must have been a serious problem, and regular shaping must surely have taken place.

Other sarsens shown on our figure seem to have had a part to play in the planning of the diagonal D, and the spine as far as the third and fourth bays. The idiosyncratic line of stakes marked E in the diagram was very probably a simple alignment on the rising Deneb—but this explanation must be abandoned if the southern ditch eventually turns out not to be unusually shallow.

Had there been only the transverse rows and the ditches, South Street would have added nothing to what has already been discovered about long-barrow astronomical practice, but a most unusual aspect of this barrow lies precisely in that very straight row (D) of stake holes that ran diagonally across it. As emphasized by the placing of the compass rose in the figure, this line has a most beautiful symmetry with the axial line of stake holes, for the angle between them is almost perfectly bisected by a north–south line.

There are two possible explanations for this diagonal, one of them almost certainly correct, the other perhaps true of an earlier period of history. If, before the barrow was built, observations had been made at the same horizon altitudes along the two lines (axis and diagonal), both to the south or both to the north, then the symmetry implies that the same star would have been seen rising along one line and setting along the other. In the case of the South Street barrow, horizon altitudes were far from being equal in any pair of the four key directions, but this offers no problem, for the stars to be seen rising and setting in this way would have been seen at their extinction angles—Pollux to the north around 3600 BC or Bellatrix to the south around 3920 BC. In either case, therefore, one could have expected perfect symmetry with respect to the north–south line. As it happens, the Pollux date falls comfortably within the range of radiocarbon dates obtained from the piece of oak found under the mound. This is surely not the date of the mound as it is now known, or of the diagonal row of stakes, but it is quite possible that the direction was embodied in some nearby material structure—say a pair of stones or another barrow. In fact at a distance of only 300 m the line runs along the southern edge of another long barrow (one of three parallel barrows northwest of the Beckhampton roundabout).

Whatever the truth of this explanation, why the diagonal line was incorporated into the barrow itself is of more immediate interest, and can be explained in a different way, not necessarily ruling out the first. It is difficult to give a precise argument for want of data from the ditches, but the rising of Regulus could have been observed along it to the northeast and the setting of Bellatrix to the southwest. Assuming that the line was regarded as very important, the entire mound could have been designed around it, with these new stars in mind. Perhaps somewhere else in the neighbourhood, or perhaps on this very site, these two stars were regularly observed along this line at equal altitudes (just over 6°) in the thirty-fifth century (point T on Fig. 37 (#ulink_214fe82f-7a44-585c-8d39-9f79cfb9209d)). Had this been done at South Street—and the radiocarbon dates tell us that this was not impossible—the mound would have been lower then, or the ditches shallower, or both; and then as the years passed, the direction no longer functioned as it had done, and it became necessary to look south at a higher angle than north in order to keep the old direction.

By 3260 BC the difference was about 0.92°. Had Capella and Bellatrix been taken as the pair of stars, it would have been found that there was never a time when they could be seen at equal altitudes along the diagonal. As the figure shows, they were much closer, however. The reason for opting for the larger separation is to be found in the ditches. It is not difficult to calculate that no matter what the height of the mound, within reason, the required difference in viewing angles would be provided if the observer looking north were standing about 33 cm higher than the observer looking south. The precise value depends on where in the ditches the observers stood, but on the evidence at present available it seems that there was probably a difference of levels somewhere between 25 and 40 cm. The required viewing altitudes for the year 3260 BC (see the figure) imply a barrow that would have been about 33 cm lower at the crossing point of the diagonal than at the barrow’s eastern end. This is precisely a quarter of the way along its length of 36.8 m as judged by the bays—note that it comes after five out of twenty bays. If it sloped regularly, therefore, the barrow would have fallen from 1.66 m at its head to 33 cm in the last bay, measuring above the base so carefully prepared for it.

These proportions are unlikely to have happened by accident, and one cannot help wondering whether the derived viewing altitude across the first bay, estimated at 9.42°, was not likewise deliberately chosen as a gradient of 1 in 6 (or 9.46°). There is much evidence from a later date for the use of such simple ratios. One can only make this assumption freely, on the other hand, if there was no other constraint, and there can be little doubt that there was one very important constraint accepted by the designers. The first four rows of stake holes on the northern side were almost certainly meant to be exactly at right angles to the axis—the average angle was around 89.8° even at the time of the excavation. This was surely the builders’ second precondition—the first being acceptance of the diagonal. It is unlikely that they waited until the old Bellatrix line (the axis) was at a perfect right angle to a one-in-six Sirius line, before setting up the barrow. Had they done so, however, they would only have been playing yet another round in a science of barrow-symmetry and precise alignment that one suspects was becoming an end in itself.

Skendleby: Giants’ Hills 1 and 2. Stars and Sun (#ulink_0069cb58-693f-57ca-83aa-d3818e8a4da2)

While the focus of attention is Wessex practice, there are other important long barrows that are worth mentioning since they reveal so much in common with it. Two of these are at Giants’ Hills, Skendleby, Lincolnshire. Both Skendleby barrows were constructed using the technique of fences of stake posts, now emphatically holding multiple horizontals (hurdling), and not only single fence-top poles. Each barrow was at some stage fronted by a façade of heavy timber posts, which in the earlier case were used to mark the extreme directions of the rising of the midwinter Sun and the setting of the midsummer Sun. Skendleby 2 long predated Beckhampton Road, and seems to have set its perpendiculars towards far edges, as did that barrow. At a later stage two other early instances will be added to our list of long barrows with solar alignments.

The two Skendleby barrows are near neighbours on the same hillside—they are only 250 m apart—and are among fifteen or so long barrows on the Lincolnshire Wolds. Skendleby 1 (latitude 53° 13' 05") was excavated under the direction of C. W. Phillips in 1934, and Skendleby 2 (latitude 53° 12' 40"), in what amounted to a rescue operation, under the direction of J. G. Evans and D. D. A. Simpson in 1975–6. It is likely that each went through at least two distinctive phases, which it will be convenient to distinguish as Skendleby 1A and 1B, and Skendleby 2A and 2B, and so forth.

Both were almost wholly surrounded by ditches, and those flanking the barrows seem at first sight to have been by no means at equal levels. Had this been wholly true it would have meant that our fundamental assumption was inapplicable, and that our method would have needed to be applied, if at all, in a modified form. (To every observing altitude from one ditch there corresponds a unique ridge height and therefore a unique observing altitude from the other ditch. Given a complete ditch survey it would in principle be possible to extend the method to such cases, matching disparate observing levels.) In fact on closer examination it appears that a ledge was deliberately placed in the lower ditch to be at the level of the floor of the upper (see the left lower part of Fig. 38 (#ulink_a474c9e0-9e2f-5b8a-b468-28e194911054)). This ledge was vital to the planning of the barrow: it was clearly cut to satisfy the general precept that observation must be at equal distances from the ridge, and from places at equal levels below it. As can be seen from the same figure, however, when the ditch was cut of necessity to a lower level, for materials, the possibility was retained of observing at precisely the same angle albeit from that lower level. At Skendleby 1 the same principle is to be seen in reverse (see the upper left of the same figure). Here the key positions for the planning of the ditch were in mid-ditch, but an additional place was provided on a wide inner ledge. Something similar was seen at the Horslip long barrow.

The excavation of Skendleby 1 was a model for its time—perhaps one day a return will be made to Phillips’ attempt to draft ditch contours—and the monument yielded good geometrical detail. Fig. 39 (#ulink_f6cb2c35-3ec8-5967-9cdc-ff3f4deb4391) abstracts what from our point of view is the most important information. The façade, in what was described by Phillips as a revetment trench, is at R. The posts in it had been split, and the flats of the semicircles set against the outer curve, to the northwest, suggestive of a wall intended to be a solid curtain. H was a large hole, B a platform for the burial, and S a line of stones, perpendicular to the axis of the barrow.

FIG. 38. Important sections of the ditches at barrows 1 and 2 (in their final forms) at Giants’ Hills, Skendleby. Both barrows run close to contours on hillsides, and the fall of the ground across the barrows is easily appreciated here. A rough idea of likely mound forms is given by the lines of sight, astronomically derived. The upper section corresponds to the line XY in Fig. 39 (#ulink_f6cb2c35-3ec8-5967-9cdc-ff3f4deb4391) and the lower to a roughly similar place on the similar barrow Skendleby 2. Key viewing positions at the planning stage were x, y, p, and q. Note the optional viewing positions, z and r, to the left (south west) of the sections.

Skendleby 2 had been severely damaged by long ploughing, but the mapping of the barrow was done meticulously, and radiocarbon dating produced no fewer than fourteen dates in all, covering a perplexing spread of time—almost two millennia. Its end-ditches were clearly meant for observation. There were actually two end-ditches at the northwest: the first had been filled in before a new one was cut about 10 m further from the façade. This might mean that the mound was at some stage lengthened—say from 60 m or less to 70 m. The former, as it happens, is the length of Skendleby 1. The deeper ditch to the front of the façade was well fitted to observation over the mound. The rough equality of the distances of observers, from side ditches to ridge, and from front ditch to façade, will eventually be used to confirm that there was at Skendleby 2 a set of three equal viewing angles.

FIG. 39. Outline of Skendleby 1 (upper figure). The contours are at 2 ft (about 60 cm) intervals, and although unnumbered, their change can be estimated with the help of Fig. 38 (#ulink_a474c9e0-9e2f-5b8a-b468-28e194911054), showing the section XY. The mound base (outer contour of hole H) is 236 ft above the Ordnance Datum. The positions of many of the revetting posts round the edge follow the conjectures of C. W. Phillips. The stake holes for the fencing of the bays, and collapsed poles, once tied to them, are at the northwest. The studied proportions of the southeastern end are intimated in the lower figure (drawn to a larger scale), where construction lines are conjectured. The width of one of our hypothetical bays is double the interval between revetting posts, that is, about 3 m.

These twin barrows provide us with an object lesson in the importance of precision, something that can be best illustrated by the fact that, while the barrows differ in direction by only a few degrees, and are of much the same form and dimensions, the star Deneb was much implicated in the design of one but not the other (Skendleby 2, but not Skendleby 1, which was begun several centuries later). There are some difficult problems here, not only internal, but of the relations between the two barrows. Even after two exemplary excavations, there is much simple but desirable surveying information that is lacking, and that might one day allow a more complete analysis.

The bowed form of the façade of Skendleby 1 seems to hint at a clever architectural device for holding back the soil of a mound. On these grounds it might be made the later of the two—and the astronomical arguments fall in with this idea. In both cases, a mere glance at the plans is enough to suggest that there are components of the barrows that are skewed with respect to the axes of the mounds. This should be enough to alert us to the presence of multiple celestial alignments.

Consider first Skendleby 2. The southern edge of the mound has been irretrievably lost, but long stretches of the northern edge are known in minute detail—for which the excavator’s report must of course be consulted—and a perpendicular to the first and best sets an azimuth of 225.7°. An average for five transverse fences of stakes on the south side gives azimuth 45.8°. Together, these suggest that the principle of setting right angles to far edges is being observed here, as at South Street. The figure of 45.8° is doubly significant, as will be seen, for the observation of Deneb. This is the first crucial azimuth.

The façade sets a good line at right angles to a row of thin stakes (see Fig. 40 (#ulink_1af62872-f102-5cbb-8e4a-18ba3d231b06), azimuth 133.8°) at its centre. It was likewise almost exactly perpendicular to four posts of intermediate size at the northeast side, which were no doubt an aid to setting out the façade, with properties to be explained. The direction of the façade is comparable with that of the front edge of the mound and that of a transverse stake fence on the northern side, but again these will be kept in reserve. It will be assumed that viewing across an unspecified mound (not the last erected there) from the northern ditch was done at an azimuth of about 223.8°. This is the second crucial azimuth.

FIG. 40. Outline of the Skendleby 2 long barrow. The coarse broken lines pick out some of the symmetries of the plan. Lines numbered 1 and 2, passing through the gap in the façade, are sight lines for solar observation in two directions. For further detail see Fig. 41 (#ulink_12510215-cb11-569e-ad13-b6e5b354f216).

Combining it with the first, in the now standard way, one finds that the rising of Deneb could have been seen over the mound of Skendleby 2A to the northeast from the southwest ditch at altitude 13.96° around 4020 BC, together with the setting of Betelgeuse at the same date and altitude, looking from the other ditch to the southwest.

In this first phase of the monument, the ditches might well have differed somewhat from the later ditches, as is known from the excavation, but it must be said that the change cannot have been great, for what is known of them fits very well with the derived viewing angle. The ditch to the front, moreover, is everything that we could wish for. By a fortunate chance, the excavators took a section almost exactly where it is needed. The short row of stake holes in front of the façade (not to be confused with the long row along the axis) meets the front ditch at a very special point indeed (Fig. 41 (#ulink_12510215-cb11-569e-ad13-b6e5b354f216)). Lines from this point to the extremes of the observation trench run due west and due north. (This is our oldest example of a more than tacit occurrence of precise cardinal points.) Not only this, but there are two steps cut into the chalk at this point (see the right-hand side of Fig. 42 (#ulink_795cc65b-47d3-5cf7-862a-99b9a4352cb0)), and from the upper step, observation could have been made over the top of the façade at the very angle (nearly 14°) to be derived from the assumption of cross-viewing from the side ditches. This angle has two remarkable properties. First, it allows the setting of Deneb to be seen in a direction virtually identical to that of the line of stakes in front of the façade, at the same date as the crosswise observation of Deneb’s rising. (The discrepancy in azimuth is about a quarter of a degree, which is of the same order as the accuracy of our present measurements.) Second, taken in conjunction with the levels of the ground and distance of the ditch, it carries the important implication that the height of the eye of a man of normal stature making the observation would have been exactly the height of the operative posts in the façade itself. In other words, the same man could just have seen over the relevant part of the façade, had he stood against it at ground level. The assumption here is that the height of the eye (E, in the figure) is made equal to that of the average West Kennet male (nominally 1.66 m).