The mosaics on the back of the arch are from the 13th century. Some were made by Byzantine artists, and some are by Pietro Cavallini. They were orginally on the outside of the façade, but were moved here after the fire. The mosaics are of the Head of Christ in the center, with His hand raised in blessing in the Byzantine manner. He is in a circle held by two angels. To the left is a winged Bull symbol of St Luke, and on the right is a confusing figure of winged Lion of St. Mark. On the sides are St Peter and St Paul seated on thrones.