Civitavecchia [ˌtʃivitaˈvɛkkja] is a town and comune of the Metropolitan City of Rome in the central Italian region of Lazio. A sea port on the Tyrrhenian Sea, it is located 80 kilometres (50 miles) west-north-west of Rome, across the Mignone river. The harbour is formed by two piers and a breakwater, on which is a lighthouse. The name Civitavecchia means "ancient town". Population was around 53,000 as of 2015.

The modern city was built over a pre-existing Etruscan settlement.

The harbour was constructed by the Emperor Trajan at the beginning of the 2nd century. The first occurrence of the name Centum Cellae is from a letter by Pliny the Younger (AD 107). The origin of the name is disputed: it has been suggested that it could refer to the centum ("hundred") halls of the villa of the emperor.

In the early Middle Ages (530s), Centumcellae was a Byzantine stronghold. It became part of the Papal States in 728. As the port was raided by the Saracens in 813-814, 828, 846 and finally in 876, a new settlement in a more secure place was therefore built by order of Pope Leo VII as soon as 854. The Popes gave the settlement as a fief to several local lords, including the Count Ranieri of Civitacastellana and the Abbey of Farfa, and the Di Vico, who held Centumcellae in 1431. In that year, pope Eugene IV sent an army under cardinal Giovanni Vitelleschi and several condottieri (Niccolò Fortebraccio, Ranuccio Farnese and Menicuccio dell'Aquila among them) to recapture the place, which, after the payment of 4,000 florins, became thenceforth a full Papal possession, led by a vicar and a treasurer.

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