The cathedral was built on an earlier 5th Century site. The façade is a mixture of Renaissance and neo-classical styles. Inside, renovations by Giorgio Challant in the 16th Century included a notable set of Romanesque fresco cycles in the loft section. A rear wall has a mosaic, of two separate periods: the 13th Century part depicts the year, months and the four rivers of Paradise, and the 14th Century part shows animals, monsters and the Tigris and Euphrates Rivers. More grotesque figures are found in the 15th Century wooden choir stalls.