The fortified town, thought to date from the 1st century AD, may have been home to 1,000 people.

Archaeologists believe the 10-hectare settlement near Wickwar, South Gloucs, was a regional trade centre.

Their investigations have already revealed the remains of an entrance gate, industrial works, a road and a large number of houses.

'No idea'

Andrew Young, of the Institute of Field Archaeology, said: "When I first visited the farm I had no idea what we would find.

"We did some research and were astonished at the extent of the ruins. It is quite well preserved."

The find came when David Isaac, whose family have farmed at Hall End Farm between Chipping Sodbury and Wickwar for more than 80 years, showed an archaeologist several Roman artefacts.

Three generations of the family had collected Roman coins, brooches, lead dice, animal bones, pottery and thimbles.