With the church closed by two apses at the far ends and no façade, you will have to go in at the side if you want to see this Romanesque basilica. It was built in the 11th century on Mount Agellu and, from Roman times, destined as a place for worship and burial. This can be seen by the pagan and paleo-Christian necropolis discovered under Atrio Metropoli, to the south of the basilica, and the remains of a 4th-5th century church which can be seen in Atrio Comita, to the north. Its impressive external forms reveal the artwork of the Pisan masters, as does the lunette above the main door on the north wall. The other, from the Aragonese school, was added in the 16th century, while its double, on the south wall, dates back to the 1400s and has the stamp of Catalan gothic. Austere solemnity, through the dim light of delicate single lancet windows, filters into the three internal naves with their columns which were salvaged from buildings of the Roman ages. The crypt, which houses the relics of the three martyrs Gavinus, Protus and Januarius, and the wooden catafalque with the statues of the three saints in the north east apse are 17th century additions.