Civitavecchia in 1795, etching by William Marlow.
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.
The place became a free port under Pope Innocent XII in 1696 and by the modern era was the main port of Rome. The French Empire occupied it in 1806. On 16 April 1859 the Rome and Civitavecchia Rail Road was opened for service. The Papal troops opened the gates of the fortress to the Italian general Nino Bixio in 1870.
During World War II, Allied bombings severely damaged Civitavecchia, and caused civilian casualties.
Louis Till, the father of Emmett Louis Till was convicted of the rape of two local Italian women and the murder of another in Civitavecchia.