Among several beautiful churches in the city is the Basilica of Saints Felice and Fortunato, who were martyred under the reign of Diocletian sometime in the third Century. There was a church built here in the fourth Century A.D. to house the remains of these two saints and there are traces even today, of the original structure, including some mosaics, despite the ravages of invading hoards and some bomb damage from both World Wars.
A hint: when you walk in the church, just to the right is a small door that will take you down to the original structure. It is not well-marked and easily missed by the casual visitor, but is more than worth the 2 Euro charge. We are not aware of any official website for the Basilica.