Photo: Portchester's location on the Hampshire coast has made it a valuable defensive outpost for almost 2,000 years. © English Heritage.

Archaeologists working at Portchester Castle believe they have discovered evidence that it was once a Roman trading port.

Topographic and geophysical surveys of the ancient site have revealed a number of previously uncharted structures dating from Roman, Saxon and medieval times.

A team of archaeologists from the University of Southampton spent two weeks surveying the castle’s outer bailey, as well as the area between the inner and outer defensive ditches.

The most revealing results, however, concerned the area outside the castle’s defences between Portchester village and harbour. This section has never been investigated by archaeologists before and turned up some intriguing findings.

"Our study of the area north of the outer ditch was an attempt to place the archaeology of the castle in context," explained Kristian Strutt, geophysical researcher from the University of Southampton.

Photo: the archaeologists' grey-scale map shows the surveyed (shaded) areas. © English Heritage.

They came across a number of features, including a spit of higher ground to the east of the village, which they believe represents a jetty for the off-loading of vessels in the harbour.

"This reinforces the notion that Portchester has been an integral shipping post for a long time," said Kristian.

"We know that in the 14th century it received exotic renovation materials, like Flemish tiles, by boat and it may have been a rallying point for the fleet during the 100 Years War. 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."

In the outer bailey features were discovered that relate to the Roman, Saxon and medieval periods of the site. Between the inner and outer ditches possible remnants of the Roman fort and a number of medieval and post-medieval structural features were detected.

Portchester’s outer defences incorporate the well-preserved remains of a Roman fort. It is thought to have been established between AD 285 and 290 by Marcus Aurelius Carausius who was instructed by the Emperor Diocletian to clear the seas of pirates.

Photo: © English Heritage.

From the fifth century, an Anglo-Saxon community settled the fort and it later became one in a chain of strongholds for the defence of Wessex.

Among the principal surviving buildings are the 12th century keep, heightened in the 1390’s for Richard II. The castle was also used to hold prisoners of war until the end of the Napoleonic Wars.

The site is owned and managed by English Heritage and Pam Braddock, Portchester Castle curator, explained how the University of Southampton got involved.

"We invited Southampton University because we are looking to widen our collaboration with external bodies, because it was good training for the undergraduates and because it gave us more information about the site," she said.

"The survey will also benefit visitors to Portchester. The information garnered will be incorporated into our new interpretation in January giving us a richer picture of the history of the site."