harbour town of imperial Rome. The artificial harbour at Portus, constructed by the emperor Claudius I (AD 41–54) to replace Ostia (q.v.), was connected to Rome by canal and the Tiber River.

After about 200 ships were lost in the harbour during a storm in AD 62, Trajan added a second harbour, a landlocked inner basin, joined to the Claudian harbour by canal. Portions of its facilities remained in use until modern times.