The Cathedral of Santi Margherita e Martino stands in the centre of the medieval hilltop town and is the principal church of Tarquinia. The current building dates largely from the 11th century, with later additions and modifications, and preserves a fine Romanesque-Gothic interior. The crypt contains early Christian and medieval sculpture, and the main nave has a wooden ceiling painted in the 16th century.
The medieval town around the cathedral is worth a walk in itself: the Piazza Cavour in front of the cathedral, the Via di Porta Tarquinia, and the streets around the Palazzo Vitelleschi give a good sense of an Etruscan-then-medieval Italian hill town that has aged gracefully without excessive restoration. Tarquinia remains a living town, not a museum piece.