File:The Nave and Apse.jpg

English: Different from most other early churches as there is a lot of light coming in through the windows. Despite being common in the ancient and medieval churches, it is hardly seen any more as the openings have often been walled up or the windows reduced in size. The traditional explanation is that medieval people believed that less light would give better conditions for prayer and meditation. However, the real motivation was concerns over the stability of ancient buildings. Smaller windows meant stronger walls.

With four of the twenty-four fluted Proconnesian marble Corinthian columns. They are dated to the 2nd century, and are all from the same origin, with high quality capitald. They were probably taken from one of the buildings on the Aventine that had fallen into disuse by the mid 5th century. They may have even come from one of the closed temples on the Aventine, such as the one of Juno. The columns show little signs of re-use, and therefore may have come unused from an imperial builders' store.

The colonnades support arches instead of trabeations, and follow the Hellenistic principles as described by Vitruvius.

The flat coffered wooden ceiling is a simple one, decorated with stars in gilt, and it was provided in 1938.