Silbury Hill (Wiltshire, England), the largest man-made mound in Europe, is 30-metres high and 160-metres wide. It is more than 4,000 years old (c 2,400-2,000 BCE), and its purpose has been a well-kept secret for at least half that time. Several years ago, a hole appeared at the summit of the Neolithic monument, around the spot where the Duke of Northumberland had sunk a shaft to carry out excavations in 1776. Further investigation showed that other tunnels from later digs were also unstable. Contracting a team of engineers to stabilise the internal structure provided a chance to gain a greater insight into date and function. The work was only completed last winter, but while it could take two years to fully evaluate the finds, it seems Silbury had a part to play in later history that no one had hitherto imagined.
     Archaeologists found a series of medieval pot-holes on top of the hill, indicating a large building. The discovery of two arrowheads also suggested it had a defensive purpose in the period of the Danish invasions early in the 11th century. There is speculation, too, that Silbury was originally dome-shaped in its prehistoric form, and that its current flat-topped aspect was the result of later lopping off to create its military function.
     So the mound wasn't simply some ghostly feature that became abandoned in prehistoric times, says Rob Harding, the English Heritage project manager for the site. According to Harding, there is also evidence of Roman usage in the platforms along the side of the hill. "Often, the Romans adopted the local gods and forms of worship when they arrived in new countries, so we think it would have had some sort of ceremonial function for the Romans. But it is possible it was disused in the period prior to their arrival in 43 BCE." As Harding admits, none of this brings us remotely closer to finding a conclusive explanation for why it was originally built. "You can rule out the idea that it formed a settlement, or an enclosure. We believe it had some sort of ceremonial or religious function, but we've found no evidence of human sacrifice or offerings to the gods, so we can't prove it."
     Bit by bit, archaeologists are piecing together elementary facts of how Silbury Hill was built. There were, it seems, three main phases. The first used stacked turf capped with clay; the second used piled rubble chalk and was undertaken soon afterwards, around 2,400 BCE. It is possible there was a gap of a few hundred years between this and the completion of the third phase. It's worth remembering that in its original conception it would have been stark white. "There is a lovely picture of it in the snow, and I think that is how it probably would have looked, this huge white hill in the landscape," agrees Harding.
     Because it's a fragile, though remarkably uneroded monument, access to the slopes and summit of Silbury is barred, but, says Harding, from the top you can see across to Avebury henge. If you visit the Sanctuary, the stone circle whose remains lie on a hill to the east, you can see across to Silbury, and the stone entrance to West Kennett Long Barrow. It's a fairly confident assertion that this great ensemble of monuments, in what now forms the Avebury World Heritage Site, formed some kind of "planned" landscape.

Source: Telegraph.co.uk (29 January 2009)