37 metres high, Silbury
Hill – which is part of the complex of Neolithic monuments
around Avebury, which includes the Avebury
Ring and West
Kennett Long Barrow –
is the tallest prehistoric human-made mound in Europe and
one of the largest in the world; it is similar in size to some of the
original purpose however, is still highly debated. Composed
mainly of chalk and clay excavated from the surrounding area, the mound
covers about 5 acres. It is a display of immense technical skill and
prolonged control over labour and resources. Archaeologists calculate that
Silbury Hill was built about 4750 years ago and that it took 18 million
man-hours, or 500 men working for 15 years to deposit and shape
248,000 cubic metres of earth and fill on top of a natural hill. The
base of the hill is circular and 167 metres in diameter. The summit is
flat-topped and 30 metres in diameter. A smaller mound was constructed
first, and in a later phase much enlarged. The initial structures at the
base of the hill were perfectly circular: surveying reveals that the centre
of the flat top and the centre of the cone that describes the hill lie
within a metre of one another.
indications that the top originally had a rounded profile, but this was
flattened in the medieval period to provide a base for a building, perhaps
with a defensive purpose. The first phase, carbon-dated to 2400 ±50 BC, consisted
of a gravel core with a revetting kerb of
stakes and sarsen boulders.
Alternate layers of chalk rubble and earth were placed on top of this: the
second phase involved heaping further chalk on top of the core, using
material excavated from an encircling ditch. At some stage during this
process, the ditch was backfilled and work was concentrated on increasing
the size of the mound to its final height, using material from elsewhere.
The step surrounding the summit dates from this phase of construction,
constructed either as a precaution against slippage, or
as the remnants of a spiral path ascending from the base, used during
construction to raise materials and later as a processional route. Few
prehistoric artifacts have
ever been found on Silbury Hill: at its core there is only clay, flints,
turf, moss, topsoil, gravel, freshwater shells, mistletoe, oak, hazel,
sarsen stones, ox bones, and antler tines. Roman and medieval items
have been found on and around the site since the nineteenth century.
Evidence exists that the hill was reoccupied by later peoples.