ANCIENT Scots fighting for freedom from invaders could have been held as hostages in the Roman Empire's only concentration camp, according to evidence announced yesterday.

The original occupants of building remains in Northumberland which have long puzzled archaeologists may have been rounded up during an uprising aimed at keeping what later became Scotland out of the Roman Empire almost 1800 years ago.

It was in 1931 that the first remnants were discovered by Professor Eric Birley at Vindolanda fort and on Hadrian's Wall, stretching 70 miles from the Cumbrian coast to Tyneside.

After the discovery of more since the 1980s, his son Robin, director of the Vindolanda Trust, based near Haltwhistle, Northumberland, believes they are the relics of a concentration camp where hostages were held.

He said: ''In my father's day, they couldn't understand their existence. No other Roman fort has circular buildings like these. It was a native, not a Roman, tradition.

''But we have discovered the whole of the second-century fort was flattened for these huts and a new garrison was built. It would have held around 400 men guarding what was here at the time of a known native uprising.''

Dr Birley felt there could have been up to 200 huts, built back-to-back in rows of five and holding up to 1000 people during the reign of Emperor Severus between 193 and 211 AD.

''We know that Emperor Severus was putting down a native rebellion in Scotland between Edinburgh and Aberdeen from 208 to 211. It appears he took hostages from the defeated tribes, like the Maeatae and Caledonians.

''If these had just been male prisoners they would have been kept in barracks but each hut is big enough for a family. They are very similar to native huts - about six metres in diameter.

''They had ovens and hearths which suggest they held family groups. Also, they had stone foundations and floors, probably built by the Romans, and would have had wattle-and-turf walls built by the natives.

''It's the only fort in the Roman Empire to have this type of hut and it wasn't known before that they had internment camps.''

Dr Birley added they had found no evidence of pottery or jewellery associated with Roman life. Meanwhile, the result of soil sample analysis is awaited as this could throw light on how occupants lived.

''They may have only been here for six months before the huts were destroyed and the new fort built on top, We assume the people were sent home when the rebellion was crushed.''

Dr Birley's brother Tony, a professor in ancient history, said the suggestion that the huts were used for hostages had been made in the past.

He added: ''They put the garrison in an annex outside and levelled the fort to put in these circular huts. It fits in with Severus's campaign. He was determined to conquer the whole of Scotland and obviously got some way towards that.

''He defeated them in the first campaign and thought he had sorted them out until they rebelled again. He then had another crack and that's where this situation of holding hostages could have come in.

''They could of course have been hostages from southern Scotland because he was reconquering that at the same time. It's all speculation. Some of the hostages spent years and years in Roman captivity and were taken back to Italy never to return home.''

He added that although the Caledonians and Maeatae came from much further north there was nowhere further north than Hadrian's Wall to hold hostages.

Dr William Hanson, a senior lecturer in archaeology at Glasgow University, said the hostage theory was a possibility, but to accept it would require

a ''leap of interpretation''.

He said: ''The huts were architecturally native in form, but Roman in construction. That has always been known, but it isn't really clearly understood what was happening.''

Dr Hanson said one theory was that the huts were built for locally-recruited soldiers to house them in a manner to which they were familiar. ''That was one possible interpretation, but if he (Dr Birley) is saying this whole fort was covered in these buildings rather than just a number of them then he may have a point.''

The Emperor Severus came to Britain along with his two sons to lead a campaign into the far north of Scotland. Dr Hanson said: ''Whether the huts are linked to that is another matter because the rebellion was much further north. It's possible, but how would you prove it. It's a leap of interpretation.''

He added: ''The Romans did take hostages, there's no doubt about that. They even took the elder sons of the leaders of native tribes as a guarantee of good bevahiour. These men were often Romanised before they were sent back.''

Severus eventually died in York in 211 and his sons returned to Rome after making peace with the warring tribes in Britain.