District of the City of Rome, Ostia Antica, according to the legend, was founded in the VII century B.C. by the Roman King Anco Marzio, although no historical source attests if this is the truth or less. The first documented sources, in fact, date back to the IV century B.C., when it became a Roman colony, with a garrison placed to defend the coast. The town's name derives from "ostium" (mouth), because the estuary of the river Tiber, used to border the northern side of the town, until a violent and destructive flood, in 1557, changed the river's course, moving it about 2 km further north. An active port, in the second century B.C., it assumed the important trading role for the citizens of the "Urbe" (City of Rome), thanks to its wheat storages; already in the I century B.C., the colony of Ostia acquired a certain autonomy and had the privilege to elect directly their own magistrates, which encouraged, therefore, an economic and population growth: the forum was embellished by the presence of: the Capitolium (an imposing temple dedicated to Jupiter, Juno and Minerva ), surrounded by several "horrea" (large stores), the Basilica, the Curia and the baths. The theater was built under the domain of Augustus and the old republican domus houses were replaced with rich villas with arcaded courtyards.
A phase of gradual decline started in the III century A.D. and was relentless in the V century, coinciding with the barbarian invasions. The population then began to move toward the inner zones, which was finalized by the foundation of Gregoriopoli in the IX century, on request of Pope Gregory IV.
The ruins of Ostia Antica, were only rediscovered in the XIX century, when Pope Pius VII ordered a massive excavation. The Italian State, then began a major reclamation of unhealthy marshes that infested the area, giving way to the recovery of the coastal area, which had been occupied, since then, only by salt mines.

Sites of Interest:
- the ruins of Ostia Antica, that can be admired from the Decumanus Maximus, a large paved road, on which developed buildings of different ages and functions, from ordinary homes in the I century A.D. to warehouses of the Republican era, a theater (which could accommodate up to 4000 people), baths, the Basilica, the Curia and several important Temples.
- the port of Claudius, which was inaugurated in 64 A.D., a safe harbor for ships from all around the Mediterranean basin, ensuring the transfer of goods on the river boats (naves caudicariae), adapted to go up the Tiber;
- the Port of Traiano, that features an hexagonal shape and is connected to the river Tiber by a canal. It was built to replace the system inaugurated in 64 A.D. by Emperor Claudius, to meet the growing needs of the City. It is currently located within the airport area of Fiumicino;
- the Necropolis of the Port and the one on the Via Laurentina;
- the remains of the oldest Synagogue in Europe;
- the Basilica of St. Hippolytus, brought to light in the 70s of the XX century, it is the most important early Christian Basilica in the port suburb. It stands on the ruins of a Roman thermal bath, evidenced by the remains of some water tanks. Inside the Basilica are preserved inscriptions and sculptural pieces of value on display in the nearby Antiquarium, between which stands out for its importance, the Carolingian Ciborium produced during the pontificate of Leo III (795-816);
- the ancient Viaduct of Via Ostiensis, which connected Rome to Ostia, presumably erected between the III and II centuries B.C.;
- the Castle of Julius II, whose implementation began in 1483 under Pope Sixtus IV and has submitted several changes in subsequent years. Seat of the papal customs, after the flood of 1557, that changed the course of the river Tiber, it was first used as a barn and then as a prison. Today it houses a museum which displays ceramics of the medieval and Renaissance periods.