Dedicated to San Lorenzo (St Lawrence), the cathedral was built in the 12th century by Lombard architects, and then rebuilt in the 16th century. Beyond its doors, adorned with bronze door panels made by Viterbo-born artist Roberto Joppolo, the visitor walks on a fine Cosmati floor mosaic. The three-nave interior, punctuated by columns with elegant capitals, houses the remains of 14th-century frescoes to the left of the entrance, while the start of the right-hand aisle houses a baptismal font dating from 1470. Further frescoes from the 15th to 18th centuries adorn the walls of the naves, the apses and the chapels, which also contain a panel depicting the Redeemer (1472) attributed to the artist Liberale da Verona, and the sarcophagus of Pope John XXI, who died in 1277 when he was crushed by the collapse of a wall of the nearby Palazzo dei Papi.