Apologies because I know I'm going over old ground here but there's been some discussion on the Stones List recently for the evidence (or idea) of an original spiral path to the top of Silbury.
The idea of a spiral path has been discussed before but I wonder if anyone has any further comments? I'll set the ball rolling by saying that I've thought for some time that the summit of Silbury was designed to be flat and, if so, it would suggest that it was used for something.
If the top of Silbury was originally designed to be flat (and used for something) you'd need a path to get up and down and it's not unreasonable to assume it was a spiral path (because, if you try going straight up, it can be quite a muddy hands and feet job and not very dignified :-)
Wally at http://www.cairnpapple.com/misc/Silbury/Silbury.htm has created a 3D image of this possible clockwise path to the summit of Silbury if anyone's interested.