A major dig close to Hadrian's Wall has revealed traces of a suspected refugee camp which would have housed tribespeople fleeing south from a breakdown of society north of the imperial border in the third century AD.

Archaeologists were initially puzzled to unearth the foundations of temporary but well-built structures on the site of an earlier fort within the sprawling perimeter of the Roman fortress of Vindolanda.

The director of excavations at the site, Dr Andrew Birley, said: "These are very unusual buildings and it looks as though they may number into the hundreds. Events clearly took place here on a large scale to lead to this sort of construction."

Records for the garrison at the "white field" between Hexham and Haltwhistle in Northumberland do not suggest Roman troop reinforcements needing so much space, with the invasion force mustering all along the wall.

The huts are also designed in a form familiar from vici – civilian settlements close to Roman military bases – but never used by troops themselves.

"Roman soldiers did not build roundhouses but were billeted in large rectangular barracks," said Birley, whose earlier work at Vindolanda has unearthed plenty of the standard army buildings.

"These are unique structures to be found inside a Roman fort. They are simple and very much the sort of housing you might expect to find north of Hadrian's Wall in this period, in settlements used by small farming communities.

"It is quite possible that what we have here is the Roman army providing for these farmers – creating a temporary refuge for the most vulnerable people from north of the wall."

"Those people may have helped to feed the army and traded with the soldiers, and would have been regarded as traitors and collaborators in the eyes of the rebellious tribes to the north – in what is now Scotland."

The refugees would have had to get over the wall itself, built in AD122-128, to escape possible persecution and death.

The fracturing of society beyond the northernmost border of the Roman empire is well-recorded in the years 208-211 to which the remains have been dated.

They were the last four years of the reign of the emperor Septimius Severus, born in what is now Libya, who led an invasion of Scotland in person before falling ill and dying in York.

Maintaining a buffer zone occupied by friendly tribes after the invasion was part of imperial strategy and would have justified heavy spending on refugee care while the fighting was under way.

Birley said: "It would make sense to bring refugees behind the curtain of Hadrian's Wall to protect them for so long as fighting continued. They would have had real value to the Romans who always protected anyone and anything valuable to them."