Description
Avebury Circle covers an area of about 11.4 hectares, and is four-fifths of a mile in circumference. It consists of an outer bank, between 4.2 and 5.4m high, built with chalk from the inside ditch which was interrupted by four causewayed entrances. A few feet inside the now partly silted-up ditch is the main stone circle, which originally contained nearly a hundred stones. In the centre of the monument are the remains of two smaller stone circles, set approximately 20 degrees west of a north-south axis. Of the three stones which originally stood in the centre of the northern inner circle, only two now survive; this feature is known as the Cove. In the centre of the southern inner circle once stood an exceptionally large stone, named because of its shape and size the Obelisk, and associated with it but still standing, were a number of smaller stones now know as the Z feature. Between the southern inner circle and the outer stone stood a single stone, the Ring Stone, only the last remains of which can be seen today. Such ditch and bank circles or "henge" monuments, often with internal timber or stone settings, of which Avebury is one, seem to be particular to the British Isles.
The difference in height between the top of the bank and the bottom of the ditch was not less than 15m, making the construction of such an earthwork alone an enormous undertaking. The great ditch today is silted up to at least half its former depth, so it is difficult to visualise its original appearance. When the archaeologist H St George Gray excavated cuttings across the ditch between 1908 and 1922, he found that the flat ditch was irregularly cut, with steep sides. In one section, dug by Keiller in 1938, it was found that the upper part of the inner side of the ditch rose in a series of broad shallow steps, marked deeply in several places by antler picks. There was a berm up to 4.5m wide between the ditch and bank, and in some places at least a rough chalk block wall about 1.5m thick had been built to retain the inner side of the bank, which has since slipped down towards the edge of the ditch.
At the four causeways, which the modern roads now cross, the banks were made higher and the ditches wider in order to make the entrances more impressive. This can still be seen at the north bank of the entrance leading to the downs.
Many construction tools had been left discarded by the builders in the bottom of the ditch; antler picks, rakes and some ox shoulder-blade shovels. Neolithic pottery of Windmill Hill and Peterborough type, and some Rinyo-Clacton or Grooved Ware lying about on the old surface had been covered by the bank. More late Neolithic pottery was found in the ditch above the chalk silting, and a few Beaker sherds.
Roughly 6.5m from the inner lip of the ditch the circle of 98 great sarsen stones were erected, brought from the Marlborough Downs a short distance to the east, probably with the aid of tree-trunk rollers and sledges. These stones were often set in holes dug through the soil but only just far enough into the chalk to give a solid footing, in six cases as little as 0.15m. However most of the holes were dug into the chalk to a depth of between 0.15m and 0.6m ( at least 0.45m should be added to allow for the erosion of the surrounding surface due to weathering since the holes were dug, to reach a more accurate impression of their original depth). Stakes were driven into the chalk in an arc at the back of each hole, to prevent excessive friction on its edge when the stone, having been raised up on timber baulks at the opposite end, was tipped into an upright position against them. When the stone was upright, the base was packed round with sarsen boulders and clay, flint or chalk. The full length of the stones it has been possible to measure is between 2.7m and 5.7m, of which 0.9-1.2m is buried in the ground, although the antiquary William Stukeley recorded a length of 6.6m for a stone which fell down and broke at the north entrance. This must have been the stone opposite vary large one now standing at the west side of this entrance, which ways nearly 60 tons. The two stones at the southern entrance are nearly as massive, and illustrate further the builder's idea of making the entrances impressive. All the stones at Avebury are natural blocks of sarsen, and none are dressed, unlike the stones at Stonehenge.
The diameter of the northern inner circle was originally about 96m and it contained 27 stones, if the average interval of 10.8m between stones used throughout Avebury is maintained. Only four stones remain visible today. Stukeley illustrates a second ring of stones within this northern circle, with a diameter of about 42m, and containing 12 stones, several shown lying fallen. Although there is now no evidence on the surface, his drawing may well have been correct; in 1964 the cutting of a pipe trench revealed a typical burning pit used in the destruction of these stones, on the circumference of this circle. An arrangement of three great stones, forming three sides of a square, and known as the Cove, stood at the centre. Only two survive; the stone on the north-east side fell in 1713. Stukeley was informed that it was "full seven yards long, of the same shape as its opposite, tall and narrow". The purpose of the Cove remains unknown, but similar "cove" structures are associated with stone circles at Arbor Low in Derbyshire and Stanton Drew in Somerset.
The southern inner circle was a little larger, about 10.2m in diameter, and it contained 29 stones, of which only five remain. Although an isolated standing stone was recorded inside the circumference, which led Stukeley to believe in the existence of a smaller inner circle here also, a sufficient area was excavated by Alexander Keiller in 1939 to disprove this. At the centre of the circle, a great stone, the "Obelisk" already lay fallen by Stukeley's time, and was afterwards broken up. His description conveys its size well: "The central obelisk of this temple is of a circular form at base, of a vast bulk, 6.3m long and 2.6m in diameter; when standing, higher than the rest". Between this central stone position and the western arc of the circle, the 1939 excavations uncovered the setting of 12 smaller stones known for convenience as the "Z" feature. Six of these were found intact, having been buried in medieval times, and six more had been destroyed, after their previous burial. They formed an irregular line running north and south, with two stones set back towards the east at either end, so that the whole formed part of a rectangle. Blocks of Lower Chalk from the great ditch, found in the stone holes, provided evidence at least that the Z feature was constructed a the same time as the bank. Further investigations of this area were stopped by the outbreak of war, leaving by far the greater part of the southern circle untouched; it is possible that the Z feature arrangement could be duplicated in reverse on the far side of the Obelisk, thus forming a complete, almost square, enclosure. This might be symbolic of a long barrow, containing a mortuary house for the burial of the dead. Four small pits were found near the site of the Obelisk, filled only with fine dark brown soil. Such "empty" pits are often found under Neolithic and Bronze Age barrows.
The broken stump of the Ring Stone was exposed during the Keiller excavations, and, in a similar way to the holes of the Z feature, chalk out of the great ditch was used as packing in its stone-hole. However, it does not appear to fit in with any plan, being on its own inside the main circle near the southern entrance. Stukeley described it a being "not of great bulk". The stump was re-erected over its own stone hole. Three further holes, in the area of the northern causeway, were found during the Keiller excavations; these were thought then to have been part of another small inner stone circle, but this theory was disproved by a more recent excavation. It seems possible that one hole at least held a stone which was removed, perhaps because of bad positioning, before the building of the main stone circle. ( F & L Vatcher 1976, p.34-38).