Archiepiscopal Museum, Ravenna

The Archiepiscopal Museum (Italian: Museo Arcivescovile) is located in Ravenna, Italy, next to the Baptistry of Neon and behind the Duomo of Ravenna. In the museum relics of early Christian Ravenna are preserved, including fragments of mosaic from the first cathedral church, and the chapel of Sant'Andrea, dating from the Gothic kingdom.

The main room, on entering, contains lapidary inscriptions as HIC REQUIESCIT IN PACE VIR SBL SEDA IGNUCUS ('Here lies in peace that eminent man Seda the Eunuch'), CUBICULARIUS or 'Bedchamberlain' to Theodoric the Great, buried 541 AD. Beneath this, by the window, a reliquary for the martyred saints Quiricus and Julietta, whose remains were carried from Tarsus, the birthplace of Saint Paul, to Auxerre and from thence to Ravenna. The depictions on its four facings are in keeping with the theme of donation: Galla Placidia placed it in the church of San Giovanni Battista (not to be confused with the church of the 'Evangelista'). They are:

The marble rosette on the facing wall is a Paschal calendar of the 6th century. Its purpose was to fix the movable feast of Easter in such a way that it might be celebrated everywhere in Christendom on the same day - no easy matter when East and West were using different calendars: the Eastern Church used the Hebrew lunar calendar, while the Western church followed the sun's cycle. Despite the decrees of the Council of Nicea in 325 AD and the tables of Theophilus, in this, as in all matters of faith, people followed their own loyalties. This calendar follows the eastern lunar cycle: LV on the outer rim, followed by AN indicates the phase of its 19-year cycle; the date then for Easter is written in each recurring phase from 532 AD to 626 AD.

...
Wikipedia