Archaeologists now believe a dozen skeletons discovered in a mass grave in the centre of Oxford may have belonged to executed criminals from Saxon times.

A team of three archaeologists have been digging in the quadrangle of St John's College in Blackhall Road, off St Giles, for nearly two weeks since the discovery was made.

The bones of 12 or 13 bodies have gradually been uncovered after a body part was discovered 80cm below ground level by diggers excavating the plot before a new quadrangle is built.

City archaeologists have labelled the find the most exciting in Oxford for nearly half a century, and predict more bodies could be found in the area.

But they cannot date the corpses exactly because the bodies were stripped of clothing before they were thrown into the mass grave.

Sean Wallis, project manager for Thames Valley Archaeological Services, said: "We were expecting to find evidence of Medieval activity, but we did not picture to find any bodies.

"I don't think anybody expected that.

"They look as if they were all young men in their late teens, and we are looking at Saxon times.

"We originally thought they could be Roman but now we think it could be more recent, based on the condition of the bodies, which survived very well.

"We have no idea how many we will find - they are still popping up."

The archaeologists' job has been made more difficult by the fact the bodies have been thrown on top of one another, rather than laid out neatly like a Christian burial.

Mr Wallis said: "It looks like a mass grave.

"The bodies have been chucked in, and it doesn't look as though there was a pit dug deliberately.

"They could be executed criminals or they could be battle victims. Some of it does look grisly. It doesn't look as if they met a particularly nice end.

"It is exciting. I've been digging for 10 years and I've not found anything close to this."

Brian Durham, Oxford City Council's archaeologist, said: "This is certainly rare. I haven't seen anything like it in the 40 years I've been digging in the city.

"The idea that they might be battle victims is possible, but I think we will only know that if we start finding war wounds on them as they remove them. They are all males of fighting age so it makes sense."

He said the 12m by 3m spot could have been some sort of memorial, and added: "These people's bodies were stored somewhere else until they had decayed a bit, and then buried quite roughly.

"There are limbs lying on their own, but they are whole limbs.

"There were occasions when young men might have got chopped up. There are a couple of occasions when Oxford was beseiged and it is a possibility they could be casualties of battle."