Alex Kirton, 19, a student at the university, was working in an area believed to be a bathhouse at Binchester Roman Fort, a site north of Bishops Auckland on the River Wear in County Durham, The (Darlington) Northern Echo reported.
"It was an incredible thing to find in a lump of soil in the middle of nowhere -- I've never found anything remotely exciting as this," Kirton said.
The sandstone head, about 8 inches high and 4 inches wide, is believed to be Antenociticus, one of a group of gods worshipped by Roman Britons on the northern frontier, archaeologists said. A similar head with an inscription identifying the god by name was found in Newcastle in 1882.
"Antenociticus is one of a number of gods known only from the northern frontier, a region which seems to have had a number of its own deities," said David Petts, an archaeology lecturer at the university. "It's also an excellent insight into the life and beliefs of the civilians living close to the Roman fort."
The Binchester site is owned by Durham County Council, which is conducting the dig jointly with Durham University's Department of Archaeology, the Stanford University Archaeology Center and the Architectural and Archaeological Society of Durham and Northumberland.
The head will be on public display during the Binchester Roman Festival on July 13-14.