Ostia Antica is the 35th of Rome, Italy, four kilometers away from the coast. It is identified by the initials Z. XXXV and it is distinct from Ostia. Ostia Antica belongs to Municipio X. History Under the Romans, Ostia Antica reached a peak of some 75,000 inhabitants in the 2nd and 3rd century AD. A slow decline began in the time of Constantine I, and the city became an episcopal see as part of the Diocesi of Rome as early as the 3rd century AD. St. Augustine passed through in the late 4th century; his mother, St. Monica, died here in 387 in a house property of the Diocesi of Rome. The poet Rutilius Namatianus also reported the lack of maintenance of the city in 414. Recent excavations, however, put the date of decline later. The city contained 26 operating baths in the 4th century and there is plenty of evidence of repairs on public buildings and the construction of new edifices. Though showing decay in some areas, the late period is one of transition from a city filled with workers employed in collecting, storing and moving huge amounts of grain, oil and wine (and other products) to feed Rome to one with the character of a seaside resort. The city remained prosperous into the 5th century, as it was the seat of the Praefectus annonae. There is expansion beyond the western and southern walls in the area of the Porta Marina. Ostia became an episcopal see as early as the 3rd century AD, with the cathedral (titulus) of Santa Aurea, erected over the tomb of St. Monica. As the centuries passed, Ostia fell into ruin but continued to provide maritime access for visitors to Rome. Saracen pirates were a frequent concern; the naval Battle of Ostia was fought off the coast in 849. Pope Gregory IV fortified the existing borough and it was rechristened Gregoriopoli. By this time, the shifting course of the Tiber had landlocked the ancient port, and the town was mainly a shelter for the workers of the nearby salt mills. In the late 15th century, the bishop Giuliano della Rovere (later Pope Julius II) commissioned the rebuilding of the main church and town walls under the direction of the architect Baccio Pontelli. The Castle of Julius II, also built at this time, remains the most striking feature of modern Ostia. The castle was abandoned after