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Silbury Hill
associated engineer
date  circa 2660 BC
UK era  Pre-Roman  |  category  Earthwork/Fortifications  |  reference  SU099686
ICE reference number  HEW 510
The largest prehistoric manmade mound in Europe. Its purpose is unknown, although tunnelling excavations over the last 200 years have established that it is not a burial mound.
The overall structure measures roughly 430ft in diameter and 130ft in height, with side slopes of 1:1.5. The mound is surrounded by a 30ft wide ditch from which construction materials were dug.
The construction of the mound is complex. At its centre is a smaller mound, 100ft in diameter, and this is surrounded and traversed by a series of walls made of chalk blocks and filled with chalk rubble. These radial and concentric chalk walls form a number of steps and benchings, about 17ft high, themselves packed with more rubble to fill out the dome.
The whole mound was then turfed over, but these excavations left a ditch with a 30ft deep vertical wall at the base of the mound. Against this wall, 2ft deep steps were created out of layers of piled chalk rubble. These were protected by a timber casing, to help maintain their shape in spite of usage, and the weather.
The ditch is now partially silt-filled, and much of the timber revetment is thus buried.
reference sources   LG/SJ

Silbury Hill