British archeologists have discovered an ancient Roman shipyard at Portus, about 20 miles from Rome.

A team from the University of Southampton and British School at Rome (BSR), working with the Italian Archaeological Super intendancy of Rome, has discovered the remains of a massive building close to the distinctive hexagonal basin or 'harbor' at the centre of the port complex.

The building was 145 metres long and 60 metres wide with 15 metre high roof, which date back to the 2nd century AD.

In a statement, University of Southampton Professor and Portus project director Simon Keay said: "At first we thought this large rectangular building was used as a warehouse, but our latest excavation has uncovered evidence that there may have been another, earlier use, connected to the building and maintenance of ships".

"Few Roman Imperial shipyards have been discovered and, if our identification is correct, this would be the largest of its kind in Italy or the Mediterranean," he said.

Portus was a trade gateway linking Rome to the Mediterranean during the Imperial period. "This was a vast structure which could easily have housed wood, canvas and other supplies and certainly would have been large enough to build or shelter ships in. The scale, position and unique nature of the building lead us to believe it played a key role in shipbuilding activities", said Keay in a statement.

In addition, supporting evidence comes in the form of inscriptions discovered at Portus. These descriptions referred to the existence of a guild of shipbuilders or corpus fabrum navalium portensium in the port.

"The discovery of this building has major implications for our understanding of the significance of the hexagonal basin or harbour at Portus and its role within the overall scheme of the port complex", said Keay.

The building underwent many changes since its construction in the time of the Emperor Trajan (AD 98-117). Excavation within one of the bays has revealed that its use changed over the centuries. Ninety years after it had been constructed, inner partition walls were added to it. Again, in the late 5th century AD, changes were made to allow the storage of grain.

Parts of the building were systematically demolished in the early to mid-6th century AD. Probably, it was a defensive measure during wars between the Byzantines and Ostrogoths (AD 535-553).