WORK to repair Oxford Castle's mound has revealed a ten-sided tower that has been hidden for more than two centuries.

The foundations of a 13th-century tower that once stood on top of the mound were discovered during work to deal with land slippage.

Excavation work at the Oxford landmark on New Road has led to a section of the tower seeing the light of day for the first time since the 1790s.

The current grass mound is the main surviving part of the Norman castle built by Robert D'Oilly in the 1070s.

The mound was originally crowned by a timber tower inside a defensive palisade reached by a bridge from the courtyard below.

But the mound was raised in height during the 13th century, when the ten-sided stone tower was built overlooking the Medieval city. It is a section of the outside wall of one of these ten sides that has now been exposed, to the delight of archaeologists.

Greg Lowe, who is leading the project for Oxfordshire County Council, said: "The emergence of the base of the tower is fascinating and Oxford Archaeology has been analysing the structure and will report their full findings when the work is complete.

"This is a postscript that we didn't expect.

"The foundations were last exposed more than 200 years ago by the then keeper of the prison, who was a keen archaeologist.

"Since then it has been very much supposition. We did not know how close they were to the surface or anything about the configuration of the tower."

"There is a little more work to do on the site than we had originally anticipated so the work will go on for slightly longer.

"This is not something that could have been planned for until we had actually cut into the mound and put ourselves in a position to do a more detailed assessment."

Arrangements are now being made to allow visitors to see the new discovery, which may be covered up again once work is complete.

Debbie Dance, director of the Oxford Preservation Trust, which spearheaded the restoration of adjoining buildings which now house the Oxford Castle Unlocked visitor attraction, said: "This is a hugely exciting discovery.

"We are keen to be able to share this discovery with everyone and are working with the council to make this happen. We have not had a chance to talk with the archaeologists yet. But at present it looks as though the foundations will only be open temporarily and may have to be covered again."

Work on the mound will continue until the end of July - six weeks longer than was originally anticipated.

Having cut into the mound, it has been discovered that there are gaps between soil layers in areas near to where current work is taking place, increasing the risk of further slippage if not repaired.