FIG. 23. Plan of the Horslip long barrow. Details of most of the inner area had been removed by ploughing. The letters indicate Paul Ashbee’s ditch sections. The broken-line trapezium represents no more than a directed guess at the outline of the limits of the barrow. The line of pits at the north western end might represent viewing positions for an earlier mortuary house on the site.
The Horslip barrow was originally perhaps of trapezoidal form, since the ditches that flank it are slightly splayed (Fig. 23). In 1743 William Stukeley described it as being ‘of large bulk, length, and height’, but ploughing after his time virtually removed all surface features. Its orientation was roughly 45° south of east, and in this direction the ground falls away. The southeastern end is the higher in relation to the surrounding ground, but the overall slope of the ridge of the barrow when it was erected was very probably between four and five degrees upwards in the opposite direction, that is, to the northwest. Observation in this direction seems unlikely, for want of bright stars, but looking the other way, over the natural horizon, the rising of Sirius might have been seen. The line is not securely known, and trees might have been a factor, but all plausible directions indicate a date within a couple of centuries of 4000 BC.
FIG. 24. Sections of the ditches at the Horslip long barrow, with labels following those of Fig. 23. The lines of sight are arrived at entirely on astronomical grounds. The verticals represent the height of the eye of a male observer of average height. The broken horizontals show the excellent levelling of observing positions, which ditches purely for quarrying purposes would not have had. The maximum height of the barrow can be judged easily enough from the suggested lines of sight, and is not indicated. The broken lines of sight are what might have been used had the ditches changed direction here, for example with a lower barrow. Note that observers’ heights may still be equal.
The orientation of the barrow can be estimated from the average direction of the inner edges of the ditches (135.0° for the northeastern and 140.8° for the southwestern), or from an interesting pair of pits (134.5° through their centres) that might well have been related to the line of the ridge itself, or perhaps to that of an earlier mortuary house on the site, as at Wayland’s Smithy. The pit near the northwest was roughly a metre square and three quarters of a metre deep; the other, about a third of the way up the ridge from the southeastern end, was circular in section and had dimensions about a third as great as the first. Other pits in a rough line following the southwestern edge are also represented in two cross-sections of the ditches, illustrated in Fig. 24.
Even from a single ditch, there are possibilities of multiple viewing positions. It is conceivable that the pits (here at b and d) are meant to add more, but the spread of a reasonably stable mound, of a height to be suggested shortly, makes it more probable that they are vestiges of an earlier phase in the history of the barrow, perhaps relating to the two pits on the axis. The ditches are interesting for their equalization of the lower levels, the places which on our basic assumption offer the ideal positions for viewing. Section E appears to be an aberration, failing to conform to our principles, and yet in the EF section there is a ledge providing viewing from the very same level. A change of ditch and barrow directions here could well have changed the requirements for viewing heights, to fit a later date, but still, it seems, the possibility of viewing at equal angles is being retained. The height of the spine of the barrow above the old ground level was perhaps around 3 m. The evidence for this comes from the astronomical possibilities offered by the lines of the ditches.
Applying yet again the principle of viewing at equal altitudes, at right angles to barrow and ditch edges, near or far, there is only one likely star to the north, namely the rising Deneb, but to south there is a choice of two, Aldebaran and Betelgeuse. The setting of Betelgeuse seems preferable, since it produces dates fully consistent with the radiocarbon date—which came from a piece of horn of red deer from a ditch fill. Taking the option of right angles to near edges, the date is 3809 BC (altitude 16.21°), while far edges give 3940 BC (altitude 12.26°). Coupling Aldebaran and Deneb, the angles would have been little changed, but the date would have moved earlier by three and a half centuries. Out of these four options, 3940 BC seems most acceptable. (The latitude is 51° 25' 58". Azimuths are taken as 50.8° and 224.7° (near) or 44.7° and 230.8° (far). The favoured declinations are: Deneb 36.76° and Betelgeuse –12.69°.)
In the case of the Horslip barrow, there is an odd piece of evidence supporting our preference. There is no chamfered inner edge to the ditch to suggest a viewing altitude, but if one tries to superimpose lines of sight on the ditch sections (as in Fig. 24) the floors of the ditches turn out to be better suited to the lower angle of view (12.3° rather than 16.2°), in the sense that they can accommodate more usable viewing positions. The sizes of the excavated ditches therefore give a rough idea of the height of the barrow, twice over, since they also provided the materials for it. They are quite consistent with the implied height of around 3 m above eye level.
The finer points of barrow construction, as illustrated by Fussell’s Lodge and Wayland’s Smithy, are at Horslip completely beyond recall. As already suggested, there was very probably an alignment down the line of the barrow’s axis on the setting of Sirius over natural ground (the declination being around –26.2°). This in itself would have been notable enough, in combination with the alignments on Deneb and Betelgeuse, but in the thirty-ninth century BC the Horslip site had another very remarkable property: the natural horizons there are not equal, but are such that the direction of the rising of Sirius was then at right angles to that of its setting. (Without tree cover the extinction angle was operative to the southeast but the altitude to the southwest was 1.26°.) In view of the Neolithic preoccupation with right-angled viewing, this would have endowed the site with exceptional importance, even though the right-angle property was relatively short-lived, and within a century or so was to be lost. But was it matched by another, which persisted?
It will be shown later in this chapter that the planet Venus, the brightest of the planets, might just have been seen when she was at her southern limit of setting, along the same direction as Sirius. The planet would have had this property already in the fifth millennium, and would have kept it long after it ceased to hold for Sirius. While it is a property to which one is led by considering the barrow, it is really one that belongs to the site. There are later qualifications to be made, in regard to a fundamental difference between Venus’ extremes of rising and setting, but assuming that the property was discovered at the time to apply to Sirius and to one or more of the four extremes of Venus (risings, settings, north or south), there would have been ample reason for building a barrow along one of the key directions. It is just conceivable that this property influenced the choice of a site for the Windmill Hill settlement in the first place.
West Kennet and its Star Chambers
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