Archaeologists excavating a mass grave in the grounds of an Oxford college uncovered what could be a monument dating back 5,000 years.

The team unearthed between 30 and 40 bodies in the grounds of St John's College, Blackhall Road, in March and returned to the site to find out more.

They found evidence of what they believe to be a 150m circular "henge" monument dating back to about 3,000BC - making it just one of about a dozen such earthworks in the country.

Sean Wallis, Thames Valley Archaeological Services project manager, said: "Henges of any size are quite rare, there are probably 100 in the country."

Mr Wallis is pictured unearthing a deer antler digging tool at the site.

Henges, which take their name from Stonehenge, are man-made non-defensive ditches possibly used for ritual or ceremonial purposes