Thousands of tourists who have viewed Silbury Hill (Wilthsire, England) over the last four and a half years, have probably been unaware of the crisis over its long term stability. From the ground the huge grass mound looks much the same as it has in recent centuries. But the hill is now desperately fragile and, like a giant Gruyere cheese, it is full of excavation tunnels and shafts that experts fear could collapse.
     In May 2000 it was revealed that a 225-year-old vertical shaft dug by treasure seekers in 1776 had started to collapse. It is likely the miners who were paid to fill in the 130-feet deep shaft simply poked branches in a few feet down from the top to support an earth plug. Five years ago the plug gave way, opening up the shaft and exposing a hole eight feet square. Within days the shaft funnelling and the sides of the hill collapsed inwards. English Heritage responded by intitially placing a temporary canopy over the hole then temporarily plugging with polystyrene topped with soil. Civil engineers Cementation Skanska carried out a seismic survey and revealed a series of unfilled tunnels and collapsed excavations.
     Since 2001 the hill has remained packed with polystyrene awaiting a long term solution. English Heritage now wants to discuss some of the conservation options that have been put forward over the last five years. The purpose of the meeting on November 26 is to consult on preferred options for conserving the monument, which forms part of the Avebury World Heritage Site.
     A spokesman said it was proposed that the final option chosen would also allow further investigation to find out more about the hill and its origins. He said: "The option chosen is to re-enter Silbury Hill via the tunnel dig to its centre in 1968, and then remove the existing collapse and inadequate backfill in the tunnel before properly filling it in. The tunnel and other voids within the hill would be filled with chalk to the same density as the surrounding mound material. The work of backfilling would take place backwards from the centre of the hill and enable contractors to remove any temporary supports left after previous excavations."
     The work would be accompanied by a thorough archaeological investigation to record all parts of the hill as they were exposed and to help learn more about how the hill was built. Monitors would be installed to keep a check on how the new chalk infill was settling in.
     Before the work can go ahead English Heritage is planning a full consultation with all interested groups ranging from architects and historians to local people. Admission to the meeting at 11am on November 26 in Devizes Corn Exchange, will be by ticket only. Applications to Beverley Ballon on 0117 975 0703.

Source: This is Marlborough (10 November 2005)