Stonehenge: Neolithic Man and the Cosmos. John North

FIG. 46. The mound area and inner ditches of the Radley long barrow, in the form of a parallelogram. The mound was limited by a narrow trench, probably before these ditches were cut. The broken lines show what is here taken to have been the ideal aimed at. The short sides are drawn here at exactly 45° to the cardinal points, differing only very slightly from what would be suggested by internal features of the ditches. The lines of sight are drawn parallel or perpendicular to the sides. Another ditch, omitted, but more or less surrounding what is shown here, was about 2 metres distant from it. Points A, B, C, D, and R are potential viewing positions for the stars Bellatrix, Deneb, and Rigel.

      The date is of course very sensitive to the chosen directions, and in all of them there are uncertainties attendant on the relatively small dimensions of the barrow. The measured azimuths quoted earlier produce a year of 3740 BC and a viewing altitude of 11.6°, with various qualifications that are hardly worth explaining. It would not be unreasonable to quote the date 3700 BC and to set the range of uncertainty as a century and a half either way. A reason will be given shortly for preferring a slightly later date.

      The broad scheme explained here, with two pairs of perpendicular sight-lines to Deneb and Bellatrix, seems to be the only viable one. (Betelgeuse with Deneb offers the only other significant solution with any plausible lines of sight, but it is in the fifth millennium.) Lines along the axis, for observers in the ditches north and south, seem to offer no alternatives, and viewing at right-angles to ditches is in any case something we have found used often enough elsewhere. But why, under these circumstances, did they not simply build a square barrow, or at least a rectangular one? Why did they produce a skewed parallelogram?

      The answer is that the axis had an importance of its own, for it was aligned on the setting of Rigel over the natural horizon. The barrow mound, following the altitudes derived here, would have been no more than 1.36 m above the eye of the ditch observers, and so no obstacle to an observer standing at ground level. As for the natural horizon, the town of Abingdon has long stood in the line of sight, but it seems likely that in Neolithic times the passage to the river in this direction would have been clear of trees, and that it is reasonable to take the extinction angle for Rigel. But what should that be? The site was not on high ground with good viewing conditions, but looked across the Thames valley. Using the norm for favourable viewing, the extinction angle would have been 1.53°. The derived declination in this case fits a year around 3600 BC. The extinction angle here could well be half a degree higher, however, which would bring the date a century later.

      The Abingdon ditched (‘causewayed’) enclosure produced radiocarbon dates in the first half of the third millennium bc, quite consistent with all estimates made here, but why are these spread over a century and a half? The most probable error is in the azimuths, which are probably all a degree too high. On this assumption, all dates fall within three decades of 3700 BC. Whether or not this is so, it seems likely that the Radley barrow is half a century or more later than Skendleby 2. This is not certain, but what does seem certain is that both made use of the same clever device for introducing the rising and setting of the same star.

      What of parallels with Skendleby’s alignments on the Sun? At Radley, there is no sign whatsoever of a solar alignment. The southern extreme of the Moon’s setting might have been observed in the same direction as Rigel’s, but this idea presupposes a level of sophistication for which we have no other evidence, and it must be abandoned. An isolated direction is no evidence at all. What is needed is evidence that other extremes were also observed, whether here or in the same general context, and this is lacking.

The Grendon Square Barrow

      The last earthen long barrow to be considered here in detail was intermediate in date and place between the solar barrows at Skendleby and South Street. It was revealed in another rescue excavation, this time in the Nene Valley near Peterborough in the seasons 1974 and 1975. This ‘short long barrow’ at Grendon, Northamptonshire, has an importance out of all proportion to the quality of our knowledge of it, for it seems to signal a transition between two different astronomical traditions of barrow construction. At first it was thought to be a round barrow, like others on the same site (which also included an Iron Age farm), for it was enclosed within a double ring ditch. It was eventually found to enclose a square structure with a façade strongly reminiscent of Skendleby 1 (Skendleby 2 was excavated only in 1975–6), and the ring ditch was seen to be a later addition. In advance of gravel quarrying on the site—which had been discovered from aerial photography—the barrow was excavated, but not completely, and an ‘overzealous removal of topsoil’ meant the loss of much information as to the sequence of construction. But in this case the very geometry of the barrow comes to the rescue, and it is in some ways reminiscent of Radley’s.

      The ‘long barrow’ components of Grendon (strictly area C, barrow V) are shown in Fig. 47, while the surrounding ring ditches are added to Fig. 48. All signs of the mound have been lost, but there is one good and one passable line from the façade, and one excellent straight inner edge to the ditch. What is more, the curved ditch opposite the façade fits closely to two arcs of circles of different radii, and the resulting ensemble of construction lines has some remarkable geometrical properties, quite independently of any assumption we might choose to make about potential astronomical lines of sight. Briefly, the angles marked x in Fig. 47 radiate from the centre of the circle bounding the inner edge of the ditch and are all equal to 22.5° (a sixteenth of a circle), while the angles marked y are at the centre for the outer edge, and are within half a degree of 60°. The quadrant made up of the four x-angles is not set to the cardinal points of the compass, but in any case these are not sight lines.

      Looking for lines of sight one may begin by taking parallels to the façade. (Perpendiculars to edges, which differ only slightly, will be considered shortly.) The azimuths are 314.5° and 125.4° (each of course might be reversed) for crosswise viewing. These at first make for uncertainty as to which stars were involved. Looking northwest, there can be little doubt that the setting of Deneb was observed, but in the other direction one might choose between Aldebaran (beginning of the fourth millennium), Bellatrix (mid-third millennium) and Betelgeuse. Following the standard procedure, the rising of Betelgeuse is indicated, with the setting of Deneb, both around 3450 BC and at altitude 12.7°. This fits well with stylistic considerations,