ARCHAEOLOGISTS are using hi-tech radar equipment to find the historic position of a wooden tower built for William the Conqueror.

In August last year, the historic mound at Oxford Castle reopened to the public following costly repair work.

A substantial part of the 900-year-old Norman structure slipped several metres towards New Road in February 2007, following heavy rain.

Contractors for the county council repaired the damage, and in May last year an excavation revealed the foundations of a 10-sided stone tower which once stood on the top of the mound.

On Monday, a geophysical survey using radar will examine the top of the mound in the hope of finding the precise footprint of the stone tower and the earlier timber version.

Tom Hassall, the archaeological consultant who is leading the project, said: “We know there was a stone tower on the mound, and a wooden one before that, and we want to work out precisely where it was in relation to the castle walls.

“When the mound collapsed, part of the castle keep was exposed at the top and that has prompted us to carry out this further investigation.

“We think the stone keep probably came down at the time of the English Civil War in the 17th century.

“It was likely to have been pulled down by the Parliamentary army so it couldn’t be used as a defensive base by the Royalists.

“We have seen drawings of the tower before it was pulled down and it was beginning to collapse — early drawings show a large crack running through it.”

Mr Hassall said he hoped that a permanent information board could be put up on top of the mound if the survey reveals significant findings.

He is working with staff from Oxford Archaeology, and the results of the survey this week are expected to lead to further archaelogical tests on the mound at the end of July, to coincide with the National Festival of Archaeology.

The mound is part of the Oxford Castle Unlocked visitor attraction created by Oxford Preservation Trust, which commissioned the £1,000 survey with the county council and Science Oxford.

Debbie Dance, trust director, said: “This is a fantastic chance to find out more about the original castle and to share it with the public now that the mound is open to visitors.

“We are delighted to be working with Science Oxford and the county council on this, and to have the chance to share the excitement with schools and young people.”