This immense early Christian basilica, built between 543 and 554, combines antique and Byzantine influences. Its three naves are separated by a row of arcades standing on marble columns imported from Constantinople, and finely carved capitals. However, the most exceptional feature can be seen in the apse and on the triumphal arch: mosaics, depicting hieratic characters on a gold background. Note the baldaquin above the altar, from 1267, adorned with Venetian style mosaics.