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.
Civitavecchia is today a major cruise and ferry port, the main starting point for sea connection from central Italy to Sardinia, Sicily, Malta, Tunis and Barcelona. Fishing has a secondary importance.
The city is also the seat of two thermal power stations. The conversion of one of them to coal has raised the population's protests, as it has been suggested it could create heavy pollution.
The massive Forte Michelangelo was first commissioned from Donato Bramante by Pope Julius II, to defend the port of Rome. The upper part of the "maschio" tower, however, was designed by Michelangelo, whose name is generally applied to the fortress. North of the city at Ficoncella are the Terme Taurine baths frequented by Romans and still popular with the Civitavecchiesi. The modern name stems from the common fig plants among the various pools. And also next to the town is the location of the cruise ship docks. All major cruise lines start and end their cruises at this location, and others stop for shore excursion days that allow guests to see Rome and Vatican sights, which are ninety minutes away.
Civitavecchia experiences a Mediterranean climate (Köppen climate classification Csa).
The Port of Civitavecchia, also known as "Port of Rome", is an important hub for the maritime transport in Italy, for goods and passengers. Part of the "Motorways of the Sea" it is linked to several Mediterranean ports and represents one of the main links between Italian mainland to Sardinia.
Civitavecchia railway station, opened in 1859, is the western terminus of the Rome–Civitavecchia railway, which forms part of the Pisa–Livorno–Rome railway. A short line linking the town center to the harbour survived until the early 2000s. It counted two stations: Civitavecchia Marittima, serving the port, and Civitavecchia Viale della Vittoria.
Civitavecchia is served by the A12, an unconnected motorway linking Rome to Genoa and by the State highway SS1 Via Aurelia, which also links the two stretches. The town is also interested by a project regarding a new motorway, the Civitavecchia-Venice or New Romea, nowadays completed as a dual carriageway between Viterbo and Ravenna (via Terni, Perugia and Cesena) and commonly known in Italy as the Orte-Ravenna.
The commune has multiple preschools, primary schools, junior high schools, and high schools. Polo Universitario di Civitavecchia is located in the city.
Civitavecchia is twinned with: