Built in the 11C on the ruins of a 4C building, this Romanesque church with its solitary campanile has a gorgeous mosaic floor from the 4C, which is one of the most lavish examples of such a floor in the whole of the western Christian community. The wooden framework and the arcades are from the 14C. The cripta degli Affreschi is home to superb Romanic frescoes; and a second crypt, the cripta degli Scavi, which contains excavated objects including some massive 4C mosaic slabs.