Tarquinia is on the main Rome-Pisa-Genoa coastal railway line, with regular trains from Roma Termini taking around 80 to 90 minutes. The station (Tarquinia station) is at the base of the hill, about 2 km from the historic centre and the Palazzo Vitelleschi; taxis are usually available at the station, or it is a manageable walk uphill. By car from Rome, the A12 motorway runs up the coast; the exit for Tarquinia is about 90 km from the ring road.
Civitavecchia, the main port for Rome and a large ferry hub, is about 20 km to the south — Tarquinia makes a good half-day excursion from there if you have a few hours between ferries.