In the following period Rome experiences an unexpected prosperity because of its unique location on the Tiber, which was navigable from Ostia up to the Tiber-island in Rome. Ostia's fate was inextricably tied with that of Rome.
During the fourth century BC Rome gets involved in several naval wars. From now on Ostia starts to play a important role as a military harbour. When, in 267 BC, Rome installed a new naval magistracy, one of the officials was permanently seated in Ostia.