Early Christian Sacral Architecture on the Kvarner Archipelago can be categorized into four groups. The first group consists of urban settlements and churches, which can be further divided into Early Christian cathedrals and other urban churches. Apsorus, Curictum, Arba and Fulfinum are ancient cities with such facilities. Among the most important are the Early Christian dioceses, however there are other urban churches as well, such as St. Mirin, St. Peter in Osor, St. Lawrence in Krk and the church of St. John the Evangelist. The second group comprises rural settlements and churches. Rural settlements are equally important for the development of Early Christian churches. Peculiar for this group are various architectural forms with diverse functions. The third group includes castrums and churches. It unites sacral buildings of strict form within the late ancient defensive structures, which were intended for the needs of the soldiers within the castrum. The fourth group covers all potentially Early Christian buildings on which further research needs to be conducted to confirm whether they are indeed pertaining to the Early Christian phase.