Built in the 11C, the largest church in the region miraculously survived the siege by the Turks. The cathedral is home to an extraordinary mosaic floor created in 1163 by a monk, Pantaleone, in which 600 000 multi-coloured tiles form a type of picture book telling stories taken from various sources. Also noteworthy is the semi-circular 11C crypt, with its three projecting apses, five aisles and 42 columns crowned with a variety of old capitals.