|
Bishop Neon decorated the interior with mosaics, dividing the interior surface into three zones of decoration.
In the lowest zone eight columns are set into the corners and support arches decorated with mosaics of the Prophets. Mosaic inscriptions and marble revetment alternately fill the wall-spaces beneath the arches.
In the second zone stucco arcades that may date from the building's foundation frame both the windows and the stucco aediculae that contain figures of 16 minor Prophets. This is in contrast to the absence of plastic articulation in the 6th-century churches of San Vitale and Sant'Apollinare Nuovo.
Finally, the mosaic in the dome is divided into two rings and a central medallion. The outer ring contains an architectural frieze of eight compartments that alternately enclose altars and thrones. In the inner ring two files of Apostles, led by Sts Peter and Paul and carrying golden crowns, move between garlands of flowers and draped curtains. In the centre of the dome above is a medallion depicting the Baptism.
The composition of the dome mosaics reflects the emergent principles of Byzantine art in which architectural space is used as a unifying element in decoration. The two outer rings produce an effect of spatial illusion, and their airy quality is reminiscent of the mosaics in the mausoleum of Galla Placidia.
Although the Baptism is dominated by its gold ground, the use of gold in the lower zones blends harmoniously with the other colours. The exquisite colour scheme of the Apostles' costumes, their tunics and mantles being gold and blue–white in an alternating sequence, exhibits a varied use of colour that is lost in later developments. On the columns in the ring below run stripes of gold tesserae, almost invisible to the eye but conferring a strong and shimmering light to the architectural scenery.
| 
