Probably completed around 2400 BC in the late Neolithic period, Silbury Hill is the largest man made prehistoric mound in Europe. It sits by the side of the A4 between Calne and Marlborough and is about a mile (1.6 km) from the village of Avebury. It covers 5 1/4 acres and is built on a spur of natural chalk. It stands 139 feet (42.3 metres) high and contains around half a million tonnes of chalk. Its flat top is 100 feet (30.5 metres) wide with a base of 550 feet (167.7 metres) in diameter.
Samuel Pepys wrote that it was called 'Selbury' after King Seall who it was said to be buried nearby. John Aubrey's interest in Avebury kindled interest in others and brought King Charles II to Silbury Hill in 1663.
There have been several excavations at Silbury Hill. The site was first illustrated by the seventeenth-century antiquarian John Aubrey, whose notes titled, Monumenta Britannica, published by Dorset Publishing Co. between 1680 and 1682. William Stukeley wrote that a skeleton and bridle had been discovered during tree planting on the summit in 1723. Probably, this was a later, secondary burial. The excavation took place in October 1776. A team of Cornish miners, overseen by the Duke of Northumberland and Colonel Edward Drax sank a shaft from the top. A horizontally shaft was dug in 1849 from the edge into the centre. Other excavations were undertaken in 1867 and 1886.
Excavations between 1968 and 1970, which was broadcast on BBC Television, determined that the mound was built in four stages, together with a ditch, during the neolithic period, but a specific purpose for the mound has never been determined.
In May 2002, after heavy rains, a collapse of the 1776 excavation shaft caused a hole to appear in the top of the hill. English Heritage undertook a seismic survey of the hill to find the extent the damage caused by earlier excavations and determine the hill's stability. Repairs were made but the site still remains closed to the public. As part of this remedial work English Heritage excavated two further small trenches and made the important discovery of an antler fragment, the first from a secure archaeological context at the site. This produced a reliable radiocarbon date of c. 2490-2340 BC, dating the second mound convincingly to the Late Neolithic (whilst not contradicting the 2750 BC date for the initial construction).
Recent work has focused on the surrounding ditch, which may not have been just a source of chalk for the hill but a purpose-built water-filled barrier between the hill and the surrounding area.
In March 2007, English Heritage announced that a Roman village the size of 24 football pitches had been found at the foot of Silbury Hill. It contained regularly laid out streets and houses.
In February 2010, letters written by Edward Drax concerning the 1776 excavation were found in the British Library describing a 40-foot (12 m) "perpendicular cavity" 6 inches (15 cm) wide. As wood fragments thought to be oak had been found. It has been suggested that this may have held an oak tree or a 'totem pole'.
Few prehistoric artefacts 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 and it seems that the hill was reoccupied by later peoples.
Silbury Hill remains a mystery….
Silbury Hill from the edge of the car park - April 2013