The Chapel of Sant'Andrea or Archiepiscopal Chapel is the only existing archiepiscopal chapel of the early Christian era that has been preserved intact to the present day. It was erected by bishop Peter II (494-519) during the reign of Theodoric as a private oratory for Catholic bishops when Arianism was the main religion of the court. Originally dedicated to Christ, the chapel was then renamed and dedicated to Saint Andrew, whose relics were transported from Costantinople to Ravenna around the mid-6th century AD.

The cross-shaped chapel is preceded by a small barrel-vaulted rectangular vestibule, entirely covered with marble in its lower part and decorated with mosaics at the top. The iconography of the mosaic decoration is of great interest and aims at glorifying the figure of Christ from a clearly anti-Arian point of view. The representation of Christ as a warrior, his monogram and his face as well as the images of Martyrs, Apostles and Evangelists frequently appear in a dominant position in various places of the chapel, thus underlining the concept of the glorification of Jesus and reaffirming the principles of Catholic orthodoxy.