Three Steps to Heaven
Hill isn't just a pile of earth. It was built - in three stages.
The first stage was relatively modest - a raised platform of chalk, clay, gravel and turf, no more than 120 feet in diameter and 15 feet high. This would have been completed about 2700 B.C.
Very shortly afterwards, the second stage swamped the original. This was a conical structure, about 350 feet in diameter and 30 feet high - surrounded by a broad, deep ditch. This stage was composed largely of chalk blocks, quarried from the hillside it was beginning to encroach on.
The third phase was begun before the second was fully finished. (You can almost hear the engineers moan, "You can't change the specifications now".)
This time, the builders used a complex honeycomb of chalk blocks to create a huge, stepped cone, with a flat top. Its diameter was extended to 520 feet, and its height to its full 130 feet.
Recent seismological research on Silbury Hill (undertaken because of fear that old excavations had weakened the structure) has revealed a spiral path to the top - rather than the stepped cone previously accepted. It seems likely that this was a processional ‘maze’ - a pattern to be walked in ritual observance.
The same survey has also revealed a radial sub-structure, suggesting that it would have had a web-like appearance.
See a representation of the structure at the Electronic Telegraph (this URL may only be temporary).
Around this structure, a new ditch was dug (the old one having been covered by the new hill. This one was even broader than the first - about 70 feet, but about the same depth (16 feet).
It has been estimated that the hill contains about 12½ million cubic feet of material, and about 6 million cubic feet was shifted to create the ditch. The work involved amounted to something like 7,000 man-years. The work was probably spread over many, many decades (with a few tea-breaks), but even so, compared to Silbury, the whole Avebury circle - rampart, ditch and stones - took only 600 man-years, little more than a minor exercise.
In its magnificent original form, Silbury probably wasn't grassed over as it is now - the chalk steps would have glowed white in this green landscape. The ditch would have been filled with water, reflecting this brilliance. There were two causeways, linking Silbury to the natural hillside nearby. However, Silbury wasn't particularly prominent in the landscape; it rests in a shallow hollow, and can't even be seen from the Avebury circle. Rather, it would have dominated the natural amphitheatre created by the surrounding, low hills.
So, what was it for? Thanks to the Cardiff University team, we can be sure it wasn't any kind of burial mound. Beyond that, there's plenty of room for imagination. Some have suggested that it is representation of The Mother Goddess (a big-bellied woman). Others invoke stranger ideas - Silbury as the focus of a vast network of ley-lines, as a landing pad for alien spaceships - take your pick. My money's on showbiz; Buzby Berkeley would have loved Silbury. He'd have had hundreds of scantily-clad starlets prancing around those steps.
And who's to say that wasn't the original intention?