Silbury - EH Press Release

Submitted by Andy B on Thursday, 17 May 2001  Page Views: 920

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English Heritage to excavate as first vital step in repairs

Archaeologists from English Heritage are undertaking an exploratory dig at Silbury Hill as part of their efforts to work out a plan for repairing the hole which has opened up on its summit.

The excavations will help English Heritage draw up a programme of remedial works as a matter of urgency for this prehistoric mound rising 39 metres high above the downland near Avebury in Wiltshire.

The work started on 14 May and is scheduled to last five days. Following a careful assessment of the area two trenches will be dug on either side of the hole. This hole was the result of the partial collapse of an 18th century mine shaft dug from top to bottom of the hill. The excavation will help English Heritage to find out why the tunnel collapsed and to ensure the long-term stability of the mound, the largest of its kind in Western Europe. The excavators will also monitor and record any archaeological deposits visible on the hill.

English Heritage's Inspector of Ancient Monuments Amanda Chadburn said: "The excavations will provide us with knowledge essential to our understanding of the hill's present condition. Together with a seismic survey it will enable us to solve some extremely complex technical problems and decide on the most effective strategy for repairs. We are actively pursuing a number of options so that we are ready to put the programme in place with all possible speed. The long-term future of a unique part of our heritage must be properly secured."

The excavation is preliminary to a 3D seismic survey which will map this and other later tunnels in the hill, the result of attempts stretching back over 200 years to unlock the secrets of this enigmatic monument. Until the exact size and position of these shafts is known, repair work cannot be undertaken in case this further destabilises the hill. The survey is due to start in early July and work on repairs as soon as possible thereafter. For Health and Safety reasons the hill is closed to the public and foot and mouth restrictions apply. Secure fencing has been erected and the hill is being regularly monitored.

Background Information

Silbury Hill, the largest artificial prehistoric mound in Western Europe, is from the late Neolithic period and radiocarbon dating indicates that it was built in several phases between 2800 and 2000 BC. It is 39 metres high, 28 metres wide at the top and 167 metres wide at its base. It is surrounded by a ditch from which chalk was dug for its construction.

No-one has ever been able to discover exactly why such an enormous monument was built (it has been calculated that it would have taken 3,000,000 man hours to complete it). No tomb has been found, though William Stukely wrote in 1743 that a skeleton had been discovered during tree-planting on the summit. The mound presumably has some kind of religious significance and forms part of the complex of ritual, funerary and ceremonial monuments which cluster round the village of Avebury and together form part of the Avebury and Stonehenge World Heritage site.

Silbury Hill was first given legal protection in 1883. It is in the Guardianship of the Secretary of State for Culture, Media and Sport and is managed by English Heritage. It is owned by Lord Avebury. It is also a Site of Special Scientific Interest because of its chalk flora.

In 1776-7 the Duke of Northumberland used miners to sink a vertical shaft down through the middle of the hill but found nothing of interest. It is this shaft that has partially collapsed. Another horizontal shaft was excavated from the base of the hill to the centre in 1849. Further excavations took place in 1867, 1886, 1992 and 1968-70. This last excavation produced valuable environmental data from floral and faunal remains, including domesticated animals.

The hole at the summit of the Hill measures about 7.2 by 5.5 metres wide and is currently 3.8 metres deep. It was originally smaller and deeper and was covered to protect it from rainfall whilst a plan for repairs was devised. Further collapses occurred indicating that the hill was far less stable than engineers had originally thought and the cover had to be removed for safety reasons and because it was no longer effective. English Heritage has been advised that no suitable cover can be erected because the area is too unstable. There are indications that this might not be the first time the hole has opened up: air photographs show that the top part of the shaft was exposed during some time in the 1920s and 30s.

It is essential to map all the holes, known and unknown, within the hill by seismic survey before we start repairs. Only that way can we ensure that these will be long-term. This is a unique and complex problem which requires a technologically innovative and sophisticated solution.