The building of the cathedral, to replace an older one, was authorised by a papal bull of Pope Urban VI in 1378.

After the radical rebuilding of the 1960s the only surviving original part of the structure is what remains of the door on the eastern side.

The façade of the cathedral was completed only at the end of the 15th century with works attributed to the Venetian architect Mauro Coducci (1440–1504).

Inside the cathedral a small painting on a copper plate by the Mannerist Livio Agresti depicting Saint John has been returned.

In the Cappella della Madonna del Popolo ("Chapel of the Madonna of the People") are frescoes by Corrado Giaquinto dating from 1750, and the painting was personally crowned by the Pope Pius VI on 3 June 1782, the first occasion in papal history.