The intrados of the southern arm, preceding the lunette depicting the
martyrdom of Saint Lawrence, is adorned with a double-perspective
meander, formed by double-round swastikas and squares outlined by
rows of white tesserae. The tiles are brightly coloured and arranged
in large fields. This type of decoration has very ancient roots. It is
named after the Meander, an Anatolian river with a winding course,
which flowed through Phrygia and into Miletus. It was used in Greek art
as a decorative motif to emphasise key points or thresholds, as seen
in the Ara Pacis in Rome. In Ravenna, it introduces one of the main
figurative mosaics and the swastika is understood to be related to the
cult of light, the sun and Christ – Sol Invictus. In the sacellum of Saint
Aquilinus, in Milan, a marble slab features this same motif, deeply
carved, and probably filled with coloured glass or glass paste, imitating
the jewellery of Oriental origin, with a vibrant mosaic-like effect.