Description of Silbury Hill
Silbury Hill stands over 30 metres high and 160 metres wide. It is not entirely circular, but has a series of straight construction lines at the bottom, possibly as many as nine. The original shape of the summit is unknown: it may have been rounded, and the present flat top may the result of later modifications.
The hill is surrounded by a wide ditch which extends in the west to form a ‘tank’ that is often flooded in winter.
Around much of the circumference of the mound, the original later Neolithic ground surface is visible as a slight change of slope, now standing several metres above the present base of the ditch. Beyond the ditch, on all sides of the mound, there are remnants of the ancient chalk ground surface.