Each niche, defined by the heavy piers, is a three arch arcade with two delicate columns,adding complexity to the central plan. Note as well the women's gallery on the second floor that is situated above the ambulatory.

The church was begun by Bishop Ecclesius (reigned 521-532) and financed by Julianus Argentarius, who spent 26,000 solidi on its construction; work progressed under bishops Ursicinus (reigned 534-536) and Victor (reigned 538-545), and the church was consecrated in 547 by Bishop Maximian. The basic design is Byzantine in conception and comprises a centrally planned octagon with seven arched niches and a square apsed chancel to the east, resting on eight piers, an enveloping ambulatory and gallery, and a narthex set obliquely to the church. The interior is richly decorated in marble and mosaic. It is the only major church from the period of the Emperor Justinian I to survive virtually intact to the present day and is one of eight Ravenna sites on the UNESCO World Heritage List.