Built originally in Romanesque style, the cathedral was largely modified in the following centuries. The façade originally had 13th-century frescoes, now housed in the diocesan museum.
The current façade is unfinished, with a 16th-century covering on the lower level, with pilasters surrounding niches containing the statues of the four patron saints of the city. The main portal has two statues by Prospero Spani (Prospero Sogari) in a style influenced by Michelangelo, portraying Adam and Eve.
In February 2009 it was announced that a Roman mosaic floor filled with scenes depicting pagan rites and oriental gods had been discovered underneath the cathedral. The mosaic pavement, which measures 13 square meters and dates to the 4th century AD, was unearthed at a depth of about 4 meters below the ground during archaeological investigations in the crypt. The size and design of the mosaic pavement suggest that it formed the floor of a huge room.[1]
The mosaic pavement has become an important piece of the Museo Diocesano (Museum of the Diocese), which exposes also fragments of ancient churches, dating back to the times of Matilde di Canossa, and a medieval bas-relief (Christ in throne amidst angels), originally located in the main altar of the cathedral.
