ARCHAEOLOGISTS believe Portchester Castle and its surroundings could have been an important Roman trading port.

That is the main discovery of the first survey carried out on the historical site near Fareham for 25 years.

Two teams of undergraduate students from Southampton University's archaeology department carried out topographic and geophysical surveys of parts of the castle site.

The results of the survey have just been made public and will form part of a new interpretation of the castle to be released in January.

They show a quay-like structure, probably dating from Roman times, buried on what is now a recreation ground to the north of the castle.

The survey also found the first image evidence of remnants of Napoleonic prisoner-of-war barracks.

Geophysical researcher Kristian Strutt said: "There appears to have been a possible quay associated with the off-loading of vessels in the harbour. This reinforces the notion that Portchester has been an integral shipping post for a long time.

"It also adds credence to the modern theory that the original Roman fort at Portchester was built not only as protection against the Saxons but perhaps also as a defended trading haven."

Using a resistance meter, which uses electric currents to build up a picture of what is buried, the team managed to record various features.

The problem has been dating them, which cannot be done unless they excavate.

Castle curator Pam Braddock asked the Southampton University team to perform the study.

She said: "We know there was a Roman building on this site - roof tiles show that. But we don't know precisely where this structure was and that is partly why we did the geophysical survey inside.

"It might be a way down but there are signs to suggest a substantial building.

"The Roman part was not just a military site. If it was a quay it could be quite fundamental to the development of Portchester."

With no excavation on the site planned - because of difficulties gaining permission on a scheduled site, a Southampton University team hopes to return next year to continuing unravelling the castle's more hidden history.

Pam added: "The problem is that this survey asks more questions than it answers."