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a Based on Hawkins (1965, Tables 2, 3, and 4). All dates are b.c., Julian Calender;these dates post date the actual time of building probably by more than a millennium. The sequence, however, illustrates the possible predictive value of the site.

a Based on Hawkins (1965, Tables 2, 3, and 4). All dates are b.c., Julian Calender;these dates post date the actual time of building probably by more than a millennium. The sequence, however, illustrates the possible predictive value of the site.

may account for the temporary abandonment of the site at various times in its history. The terminations of such series (here, 2039 or 2104 b.c.; cf., Robinson 1983, p. 128) may provide an important way of dating archeological monuments.

Of course, there is no direct evidence that the Aubrey holes were actually used for eclipse prediction, nor is their use strictly necessary, because the rise azimuths of the Moon provide the principal clues. The argument is one of plausibility only. The alignments are evidence of interest in lunar and solar phenomena. By association, the placement of particular stones in particular holes with the moonrise over various foresights in what later became the Avenue could have served as an early-warning device for that terrifying phenomenon of the ancient world, the eclipse. Such a warning device could serve well in periods of bad weather when close observations of the Moon's behavior were not possible.

The recognition by the builders of the astronomical significance of the number 56 is critical for the hypothesis that the Aubrey Holes were used to determine eclipses. Against the idea of the Aubrey Holes as an abacus or computer is the circumstance that while 10 other sites in Britain have chalk circles associated with henges, none has 56 of them (Burl 1987, pp. 86-88). Their numbers range from 5 for Llandegal in Gwynedd (Wales) to 44 or 45 for Maumbury Rings in Dorset, but all the others number between 7 and 14. Moreover, Burl (1987, pp. 89-90) argues that the number 56 may be an artifact of the layout of the Aubrey Holes (investigated by Thom and Thom 1974): At each of the cardinal points, two stones nearly (within 1/2 degree) flank the cardinal directions. If 12 other stones are placed between these pairs, the number 56 falls out immediately. The 12 is somewhat arbitrary but does give approximately even spacing. Burl (1987, p. 90) also points out that both the radius of the Aubrey Hole ring (which he gives as 141.4ft = 43.7m) and the separation between stones (16.3 ft = 5.0m) are not even multiples of the "Megalithic Rod" (6.8 ft = 2.1 m), at 20.8 and 2.4 MR, respectively); Thom and Thom (1973) had found, however, that the length of the circumference amounted to an even 131 MR. Whatever the purpose, Newham (1972) noticed that the length of the chord joining every other Aubrey Hole was about 1/3 that of the radius of the Aubrey circle. Once the circle had been established by means of a rope anchored at the center, and marked, the rope could have been folded in thirds and this length laid out as chords across the perimeter. In three turns around the circle, 56 holes could have been marked.

In the next major phase of construction, "Stonehenge II," a double ring of 82 "bluestones" (principally dolerite and rhyolite rocks and modified volcanic ash, but other types are also present) was erected in features called Q and R Holes. These stones all seem to come from a localized region in the Prescelly Mountains in Pembrokeshire in Wales (Atkinson 1979, pp. 49, 51). Because bluestone chips are not found below the (current) middle layer of the ditch, and there only sparsely at a level consistent with mere transport to the site (Atkinson 1979, p. 72), it is clear that they were erected later than were the features ascribed to Stonehenge I. The Q and R Hole circles have diameters of 86 ft (26 m), and 75ft (23 m), respectively. Finally, during Stonehenge II , the ditch was further filled in on the eastern side and the "causeway" was extended into an "Avenue" beyond the monument, toward the River Avon, with a new net orientation: to the midsummer sunrise.

Stonehenge III is usually considered to have developed in three substages. The first, Stonehenge IIIA, saw massive reconstruction activity, which involved the transporting of the huge sarsen stones from Marlborough Downs, near Avebury, some 20 miles away. This period involved the dismantling of the double bluestone circle, and the subsequent erection of five massive sarsen trilithons (three-stone combinations with mortice and tenon anchoring the top stone slab) in a horseshoe pattern open to the northeast. The horseshoe is encircled by sarsen stones, also possessing lintels, some of which are still in place. The upright components of the horseshoe trilithons weigh as much as 30 tons and the transport of these 80 sarsens represents a considerable engineering feat, involving as many as a thousand laborers over several years. See Atkinson (1956/1979) or Hawkins (1965) for informed speculation about how this could have been done.

Carvings of thirty axe-heads and a hilted dagger have been found on the sarsen stones. The dagger shape most resembles that of daggers found in Shaft Graves at Mycenae in Greece, with dates prior to ~1500 b.c. (Atkinson 1979, p. 92). Atkinson (1979, p. 93) states that grave goods of Wessex Culture burials "provide clear evidence" for trade with Greece in this period. Moreover, axe cults are known to have been widespread (as in Minoan Crete) in this period, but axes are also carved in tombs in Brittany and elsewhere in England. The Stonehenge axe carvings closely resemble bronze axes manufactured in Ireland and brought to England between 1650 and 1500 b.c. We recall our earlier discussion of axeheads, and note that associations with lightning or with the Sun are possible here also.

In Stonehenge IIIB, the bluestones that formally occupied the Q and R Holes were prepared and perhaps temporarily set aside, whereas a new set of holes (the Y and Z Holes) were created in concentric circles outside of the sarsen stone circle. There were 60 (or 59) of these holes, with the Z holes lying closer to the sarsen circle. However, it does not appear that the bluestones were ever set into these holes.

In Stonehenge IIIC, the remaining 22 bluestones were reset into a ring just inside the sarsen ring, and into a smaller horseshoe of trilithons within the sarsen trilithons.

Other features of the site include the fallen "Altar Stone," a 16-ft long, relatively narrow (3V2ft x 1/2 ft) block of green sandstone, speckled with mica, from a site near Milford Haven in SW Wales (not from the slightly more distant Pres-celly Mountains) near the central sarsen trilithon. Its exact intended placement in the monument is not known. A four-stone "portal" of very large stones commanded the entrance to the site from Stonehenge IIIA until at least the mid-17th century (Burl 1993, p. 39). Of these, only the so-called "Slaughter Stone" is still in place. This portal constitutes a striking similarity to portals found in the great circles of the Lake District, although Burl (1993) is unwilling to suggest that the Cumbrian circles were prototypes of Stonehenge III. However, the Lake District circles were standing even more impressively then than now, and the influence could have been transmitted by an individual of the Stonehenge community who had seen one and liked the idea.

It seems impossible that precision alignments could have been made with the massive, irregular stones of the monument as either backsights or not-so-distant foresights, although rough approximations to the solar and lunar standstills could certainly have been made. Atkinson (1979, pp. 94-96) in discussing and refuting Lockyer's (1909) theory that the midsummer sunrise alignment along the Avenue matched precisely in 1680 b.c. argues that the alignment if determined by observing through spaces of several feet between the sarsens could not possibly give a precise date for the obliquity, because a movement of 1 in would change the date by 200 years, and that by using, say, the right eye instead of the left would shift it by 500 years! It seems likely, however, that the postholes of the earliest phase of Stone-henge could have held smaller and therefore more useful foresights in combination with smaller backsights, or the posts of the entrance way could have been used as backsites by observers near the center of monument in connection with distant foresights. Brinckerhoff (1976) has suggested that pits on the lintels of the great stones in the Sarsen Circle facing the Avenue could have held small wands to be used as foresights, in a manner suggested for the posts of the Causeway during Stonehenge I. The hypothesis requires a backsight across the Sarsen Circle from a now missing lintel. Alignments to northern, major standstill moonrise and to the summer solstice sunrise both at ~2000 b.c. could have been established in this way. Systematic departures of ~0°2 from alignments with the Causeway postholes were attributed to a change in the obliquity of the ecliptic (see §2.3.3) over the approximate thousand-year interval between Stonehenge I and IIIA. More distant foresights have been proposed also. Alexander Thom (1971/1973/1978) argued that at many sites, especially in Scotland, a relatively high order of precision was achievable, and apparently achieved, by the use of backsights far removed from the observing platform and foresights on a distant horizon. Thom designed a method by which the builders or users of the sites could have sufficiently high-precision measurements of the position of the Moon to detect the 9 minutes of arc variation in the Moon's inclination. The Thoms suggested several places in the vicinity of Stonehenge from which distant foresights could have been set up (Peter's Mound, summer solstice sunrise; Coneybury Barrow, southern minor standstill moonrise; Figbury Rings, southern major standstill moon-rise; Chain Hill, southern major standstill moonset; Hanging Langford Camp, southern minor standstill moonset; Gibbet Knoll), but some of these places would have been obscured by an intervening ridge and would have required artificial foresights to have been placed on them. See Wood (1978, pp. 178-181) for a thorough discussion. We review the method in a later section (§6.2.15); at present, we discuss the evidence from some carefully studied sites.

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