The first Cathedral was built, according to tradition, in present churchyard. The plant is Latin cross, the bell tower is embedded Roman plaque mentions Gens Fabia from Veio, a title that it fell to the population since the foundation of the municipium in 49 BC. The facade onto which the three portals is incomplete. The interior is divided into three naves: the central nave there are two large domes, an elliptical, in correspondence with Chapels of St. Gregorio Barbarigo and St. Lorenzo Giustiniani and more circular cruise in the mail. Along the aisles open chapels. Under the presbytery they are placed the crypt and Chapel of Holy Cross. Among the organs is the main altar by Daniel Danieletti (1770) topped by the canopy by Cesare Bovo. Wooden choir by Filippo Parodi. New presbytery, realized on the occasion of the tercentenary of the death of St. Gregory Barbarigo, is by Giuliano Vangi and is in Carrara marble. Crypt houses the remains of St. Daniele Martire inside Roman urn placed under the altar.