Nave looking southeast. The basilica has a tall and wide nave with side aisles. There are 58 wide windows, including five in the apse, which flood the interior with light. The nave is supported on two dozen slender marble columns topped with Byzantine carved capitals. These are not ancient spoils, but a perfectly matched set made specifically for the church in the imperial workshop of Proconnesos.
Originally the nave walls and clerestory were covered in mosaics (as can still be seen at Sant'Apollinare Nuovo) but these have all disappeared. The lower part of the wall and the spandrels of the arches are now decorated with frescoes and stucco of the 18th century. The fresco medallions depict bishops of Ravenna.