In the 17th century, the antiquarian, John Aubrey, noted that Avebury far surpassed Stonehenge ' as a Cathedral doth a Parish Church'. Sir Richard Colt Hoare was also much impressed and wrote, in Ancient Wiltshire (1812): 'With awe and diffidence I enter the sacred precincts of this once hallowed sanctuary, the supposed parent of Stonehenge, the wonder of Britain and the most ancient, as well as the most interesting relict which our island can produce'. Of the four Wessex 'super-henges' which are more than 300m across, Avebury earthworks are by far the most impressive today. They also contain some of the largest megaliths in Europe. The area has been inhabited by villagers for about 1000 years. And so it comes as a surprise to learn that it remained unknown to outsiders until Aubrey rode through the village on a hunting trip in 1648.
In about 2600 BC, or about 2000 years after the first farmers reached Wessex, the building of Avebury began. They chose a lowland plain at the foot of the Marlborough Downs. Like most henges, the site is close to water, in this case the infant river Kennet. Using antlers as picks, the shoulder bones of cattle as shovels, and woven baskets, gangs dug out the ditch and threw up the bank outside. The precise shape was not important. It would have been simple to define an exact circle with rope stretched tight from the centre, but it seems that the priests who first marked out the sacred enclosure were quite content to pace out a shapeless ring. If geometry was insignificant at this stage, the scale of the tremendous scale of the excavation was clearly vital. 120,000 cubic metres of solid chalk were dug from the ditch at Avebury, a volume about 60 tomes grrater than the spoil from the ditch at Stonehenge. Only one earthwork can compare in size to Avebury, the 250,000 cubic metres of chalk and soil excavated to form Silbury Hill, just 1.5km to the south of Avebury. The two biggest Neolithic earthworks in Europe somehow form part of the same riualistic landscape.
After digging at Windmill Hill, Alexander Keiller bought Avebury and carries out a campaign of exemplary excavations through the 1930's. His team revealed how far the ditch has filled up since it was dug. When looking into the ditch today, visitors need to realise that it was first dug out no less than 6m below the level of the present turf. Imagine the bank perhaps 5m higher than today, faced on the inside with a wall and gleaming white fresh chalk, and you have some idea of its original appearance. The four modern roads still enter the henge through the original gaps in the bank and causeway across the ditch. The west Kennet Avenue still leads into the South entrance and the former Beckhampton Avenue began at the west entrance.
It has been estimated that there were originally a minimum of 247 standing stones within the henge, and perhaps 400 more forming the avenue outside. The heaviest remaining megalith, the Swindon Stone near the north entrance weighs about 65 tonnes, but the survivors average about 15 tonnes. The Avebury stones are sarsens of the same geological type as those of Stonehenge. At Avebury, the sarsens were selected for their shape and used in their natural state, whereas those at Stonehenge were laboriously worked into a precise geometry. The Avebury builders prefered their stones to be columnar or flat with a triangular outline.
The transport and erection of these stones in about 2400 bc represent one of the great triumphs of prehistoric building. Experts agree that they once lay on the surface of the surrounding hills and valleys, especially the Marlborough downs. Neolithic and more modern builders have removed all the natural boulders from the surrounding countryside but, if you follow Green Street out of the henge to the east, a chalk track will take you 3km to the main source area. There on Fyfield Down, around map reference SU134706, natural sarsens still litter the lonely sheep walks, although the heaviest ones were taken 4000 years ago.
It is natural to wonder how the huge stones were moved and erected. A knowledge of the available technology makes wooden rollers the most likely method of transport, with the exact route chosen to avoid steep and dangerous gradients. Once at their site, a small socket, only about 1m deep, was dug into the chalkand lined with wooden stakes to guide the foot of the stone into the correct position. Ropes, wooden props and levers gradually raised the stone to the vertical in its socket. This was a laborious process - an experiment by Alexander Keiller's team in 1934 showed that 14 untrained men would take four days to erect one small flat stone using Neolithic methods. Great care was taken to place the centre of gravity directly over the middle of the hole. The final act was to ram a hard packing of chalk, flints and small sarsens around the base of the megalith to hold it firmly in its socket. The stability achieved is particularly impressive in the case of the great Swindon Stone which has spent 4000 years balanced on one corner with only a fragment of its bulk under ground.
The builders chose to raise three sacred circles inside their temple. Despite their popular name, prehistoric circles are very rarely circular. This is certainly very true of the Great Circle, which follows the irregular plan of the henge, keeping a constant distance from the inner lip of the ditch. Originaly it must have consisted of about 98 stones, but their partial destruction means that we can no longer tell if the columnar or triangular stones were placed at random or in some meaningful pattern.
The huge size of the Great Circle allows ample space within it for the two separate circles, while in turn each of these could accommodate Stonehenge. In contrast with the general outline of Avebury, they are both exactly circular. The sequence of erection of the three stone circles remains unclear.
Both of the inner circles have the same diameter (103.6m). According to Alexander Thom's Theory of prehistoric surveying, this is exactly 125 'megalithic yards' and the builders used in these circles a value for Pi of 3.140, only one part in 1,975 from the true value. Although they are the same size, the two circles contain very different ritual features. The centre of the southern circle was emphasised by an obelisk, a particularly tall stone with a height of 6.4m. Its site is now marked by a plinth. Stukely drew it lying on its side in 1723, but all that was left for Keiller to record in the 1930's was the large burning pit used to break it up. A similar fate befell 24 of the 29 stones that were once evenly spaced around the southern circle. The obelisk is made more unusual by forming the centre of a mysterious D-shaped setting of small rough sarsens, the so-called 'Z' feature, which partly survives.
The northern circle is just as fragmentary - only four stones survive from the original 27 - but the ritual element at its centre is more complete. The rectangular cove survives as a three sided setting of stones. The 'Devils Brandirons', to use its popular name probably imitated the burial stall of a megalithic chambered tomb. But instead of being hidden under the dark earth of a barrow, the Avebury cove is a giant niche open to the sky, the setting for some public ritual of death. Such rites seem to have been widespread: other coves, such as Stanton Drew in Somerset or Stenness in the Orkney Isles, either lie within or close to stone circles.
The Avebury temple remained in active use for about 700 years. Towards the end of this period c.2000 BC, the 75 Stonehenge sarsens were collectedfrom the rich source on the Marlborough Downs. The difficulty of fording the River Kennet further downstream raises the fascinating possibility that these sarsens were a gift from the Avebury people and passed through their completed temple for the priests to sanctify them. Rodney Castleden believes it likely that Beckhampton Avenue was actually built to celebrate the first mile of their long and ponderous journey to Stonehenge.