Walking along the ambulatory of San Vitale’s church you can see, in the south-west area of the building, a small basin with three steps (often confused with a baptismal font) and, a little further on, a mosaic panel leaning against the church’s perimeter wall, here proposed in the photo. These two elements are the preserved evidences of the San Vitale’s chapel, a small building built in the place where, according to tradition, the homonymous saint was martyred.
It is known that the current church was built by the will of Bishop Ecclesius after his return from Constantinople, however in the area there already was small places of worship built in the placidian era and, currently, incorporated into the monument. In 1911, during the excavations carried out in the church’s ambulatory by the superintendent Giuseppe Gerola, were found a fragmented mosaic floor and the base of the original altar. The lacerto, which is 1.18 m long and 1.04 m high, presents a subdivision in three areas: the first consists of an oblique network of swastikas; the central panel, where was placed the altar, is decorated with the representation of a kantharos surrounded by vegetal elements and peacocks in the lower part and, in the upper part, with a two-headed braid; the third part is partially preserved and the whole parts are enclosed by a frame with tesserae arranged at edges.
Basing on the dimensions of the mosaic and on the wall structures highlighted during the excavation, Gerola hypothesized that the building presented itself as a single rectangular environment, developed for 4.40 m in length and 2.50 in width and equipped with an altar. This building reconstruction’s proposal did not convince scholars, who hypothesized that the excavation had found either part of the hall or the rectangular apse. In fact, the subsequent excavations confirmed this suspicion and allowed a more complete building’s reconstruction, which extended for 8.48 m in length on the inner side and had rather thick walls of about 90 cm. This fact, if compared with the walls’ thickness of the Galla Placidia’s Mausoleum (about 80 cm), allows us to hypothesise also the type of roofing: probably a barrel vault similar to that present in the placidian Mausoleum. The excavations have also highlighted the lateral enlargement interventions, dating to the twenties of the sixth century, creating a cross plan similar to that of the mausoleum by Galla Placidia.
The construction of the San Vitale’s church suppressed the ancient sacellum, but the respect and devotion to the small building was such that it wanted to preserve its memory in some way. The unusual inclination church’s narthex meets this need: if one of the entrances, in fact, is perfectly aligned with the apse of the basilica, the other is instead placed frontally to the apse of the suppressed place of worship.