British archaeologists say a dig in Italy has uncovered new secrets of Portus, a once-mighty port that served as a gateway to Rome. Built by the emperor Trajan in the second century, Portus could host 350 ships at a time bringing grain, wine, oil, slaves and luxuries to the Roman capital from all over the far-flung Roman Empire, they said. Although the mile-wide main basin of Portus has now silted up, an inner, hexagonal basin still exists as a lake situated at the end of a runway of Rome's Fiumicino airport. One mystery that has baffled historians is why the port's impressive palace and huge warehouse seemingly vanished overnight in the 6th century. An excavation led by a team from the University of Southampton has revealed Portus was systematically demolished by the Byzantines, the eastern emperors engaged in a war with the Ostrogoths to regain control of Rome. "By the 6th century the Byzantines felt the port could be a threat as it was vulnerable to being occupied by the Ostrogoths, so they took the decision to destroy it themselves," head Southampton archaeologist Simon Keay told The Guardian. The Byzantines gained and lost control of Portus several times during their war with the Ostrogoths, he said, leading to their final decision to destroy it -- not an easy task. "These were solid structures, and you really must have wanted to pull them down," Keay said. "It will have needed a firm decision and the Byzantines will have really worked on it. "Portus was a great hub, but as Rome wound down, Portus mirrored it."