Having an open connection with the sea, the Tiber didn't give sufficient protection to the sea vessels. With the expansion and needs of Rome, traffic on the river grew bigger and bigger. There was hardly space for manoeuvring on the 100 m. wide river. Silting of the river was another problem. To guarantee the supply of grain for Rome the emperor Claudius started in
42 AD to build a new harbour some two miles north of Ostia, Portus. Two curving moles were built out into the sea. Between the moles, on an island formed by the sinking of a large merchantman, a four-storied lighthouse was placed. Round about 110 AD the emperor Traianus enlarged the new harbour with a large landlocked inner hexagonal basin. The harbours were connected with the Tiber by channels.