In the same place as the present Renaissance building, there used to be three churches built in the fourth century and dedicated to Christ the Saviour, to Saint John the Baptist and the Virgin Mary. The liturgical space dedicated to the Baptist, who initially served as a baptistery, was enlarged during the Longobardic period and, over time, was preferred to the Savior, hosting the Bishop’s chair. The Diocesan Museum, open in the basement of the Cathedral, shields the archaeological remains of these ancient buildings.