Cathedral is Romanesque temple readjusted with Gothic, Renaissance and Baroque elements. Inside is remarkable masterpieces of sculpture and painting, including the tomb of SS. Mario and Martha and their children Audiface and Abaco, originating in Persia, called "Ark of Persian martyrs". The building was built in the twelfth century, a period of great prestige in the city. The main facade is clad in white Carrara and red Verona marble, characterized by a large rose window work by Giacomo Porrata from Como. The whole building is topped with numerous spiers of Nordic inspiration. The interior has three aisles separated by two series of circular cruciform pillars that support Gothic ogive. Above the aisles, they open up the matronei, watching on the main aisle through large windows. The nave ends in a large semi-circular apse, in whose basin was achieved a remarkable fresco of Redeemer. Under the presbytery there is the crypt excavated in Romanesque period.