Scanners probe Stone Age mystery

Silbury Hill is the highest man-made mound in Europe

By BBC West of England correspondent Jane O'Brien

Archaeologists are using computer imaging to try to solve one of the biggest mysteries of Stone Age Britain.

Silbury Hill in Wiltshire is the biggest man-made neolithic mound in Europe - but nobody knows why it was built.

The 130ft foot grassy mound, which was built more than 4,000 years ago, has been seriously threatened by a hole which appeared in its summit in May last year.

As repairs get under way English Heritage wants to carry out a seismic study of the hill to create 3D computer images of what lies inside.

A hole appeared in the hill's summit last year

First they have to shore up an 18th century shaft from a previous excavation that collapsed several months ago.

It has already been reinforced with polystyrene, and on Thursday helicopters will transport 36 tonnes of chalk to cap the opening.

Once the hill has been made safe, four small vertical holes will be bored into its side so that scientists can increase the detail of the interior scan.

The results should be known in October. Archaeologists have tried to uncover the secret of Silbury Hill for more than 200 years.

Archaeologists will use an 18th Century shaft

The giant mound would have taken 700 men 10 years to complete, using antler picks and shovels made from the shoulder bones of animals.

There have been several theories about the site, which forms part of the ancient landscape surrounding Avebury stone circle and nearby Stonehenge.

No evidence has been found of any human burials but many believe it was a sacred monument.

Others think it was nothing more than a Stone Age waste tip.