The early Christian Oratory (6th century. A.D.), built by command of Opilione, Theodoric's Prefect, has the typical form of the martyrium, a Greek cross preceded by a little narthex.
The terrible earthquake of 1117 destroyed its beautiful mosaics, which narrated the life of the Bishop St. Martin.
The most important things to see are:
1) the Tomb of St.Prosdocimo, with the image of the saint in the typical ravennate style of the 5th/6th centuries.
The Saint Bishop, as the tradition goes, lived between the second half of the 3rd century and the first half of the 4th century, at the time of St. Giustina.
2) The marble tympanum bearing an inscription by Opilione (6th c.).
Of great interest the two crosses, which have Greek letters, building a figurative language symbolizing the passage from death to life and the image of Christ as Lord of the Universe.
3) Two pluteus, which probably belonged to the early Christian basilica. They are decorated with vine-shoots, doves, peacocks, etc.