The primitive structure dates back to 1075, but the façade as it is was modified in 1463. The two majestic towers are original only in their lower part. The right tower was modified in 1532 by the council, that had the belfry window carried out, and also obtained the bishops permission to put a clock in it. The left one was the true belfry, and originally had a three-mullioned window on three sides and a one-mullioned window on the western side. The building is accessible through a staircase, as a result of the square raising; its got a latin cross plan with perimetral chapels, surmounted by groined vaults. Decorations are in neogothic-byzantine style, while frescoes date back to the 14th century.A splendid 15th century Annunciation was found in 1980 in San Giovanni’s chapel during some restoration works.