Photo: at 39 metres (about 130 feet) high, Silbury Hill is said to be the largest prehistoric artificial mound in Europe, comparable in height to the great pyramids in Egypt © English Heritage and Skanska.
Ever since a hole appeared, Silbury Hill has been a topic of heated debate.
In May 2000 a hole emerged at the top of the mound after a period of prolonged heavy rain. Over the weeks that followed it opened into a wide breach thought at one point to be over fifty feet deep.
Four years after the collapse the debate rages on. English Heritage, charged with the care of this impressive Neolithic mound, has according to protestors not done enough to secure its future.
Photo: aerial photo of Silbury Hill taken by English Heritage in February 2001. © English Heritage. Photo: Damian Grady
Heritage Action, a pressure group made up of ordinary members of the public who feel heritage protection is sometimes not as effective as it should be, claim Silbury Hill is in peril and that there has been a series of further collapses since May 2000.
"Silbury Hill is a unique construction often trumpeted as the greatest prehistoric mound in Europe," said Nigel Swift, a spokesperson for Heritage Action.
"But it has been four years since the collapse. We feel it is essentially a structural issue first and an archaeological issue second and we consider English Heritage has got the balance wrong.
"As a result time spent, which exceeds time spent tunnelling to France, has been excessive. We fear the tunnels and the centre of the mound are not fully stable and every day risks further loss of archaeology."
Photo: English Heritage archaeologists beginning an exploratory dig as part of their plan to repair the hole in the hill, which appeared in May 2000 © English Heritage
Built between 2800 and 2000 BC, the same time as the Egyptian pyramids, Silbury Hill is part of the Avebury World Heritage Site.
Covering an area of 22km square, Avebury World Heritage Site includes 345 archaeological sites, 68 Scheduled Ancient Monuments and five Guardianship sites and is believed to have some kind of religious significance.
Silbury Hill itself has been designated a Scheduled Ancient Monument by English Heritage and is also a Site of Special Scientific Interest.
Photo: English Heritage used a helicopter to dump tons of chalk on Silbury Hill, Wiltshire, in an effort to stabilise one of the most puzzling archaeological sites in Europe.
The first recorded archaeological investigation of Silbury took place on October 31 1776. Miners dug through the centre of the mound and the worry is that the tunnel was not properly backfilled when work was completed and this is thought to be the cause of the collapse in 2000.
Since its collapse English Heritage have carried out a series of investigations and repairs to the mound including filling the hole with polystyrene blocks to support the sides.
Commenting on the criticisms by Heritage Action, a spokesperson for English Heritage said: "We welcome input into our work and value the importance the public attaches to the nation’s heritage, including ancient monuments like Silbury Hill, but we do not accept Heritage Action’s claim that Silbury Hill is at risk of further collapse. The results of our investigations have shown that the Hill is fundamentally stable.
Photo: Silbury Hill at dawn. Photo by Dave Field © English Heritage
"We are working towards a solution to conserve Silbury Hill for centuries to come. This is necessarily a complex and lengthy process given the unique nature of the archaeology on the site. We will be announcing a number of conservation options for Silbury Hill later in the year, when a full risk assessment in relation to each one has been completed.
"Our Chief Executive has responded to the concerns of the Heritage Action group in writing and members of Silbury Hill project board have offered to meet with the group to address their points in person. We look forward to working with the group constructively in the future."
Heritage Action will be staging a protest on May 29, called the Fourth Anniversary Protest, it begins with a march from Avebury to Silbury followed by an open air conference.
To find out more about Silbury Hill click here to visit English Heritage’s website.