Christianity was present in Roman Britain from at least the third century until the end of the Roman imperial administration in the early fifth century, and continued in western Britain.
Religion in Roman Britain was generally polytheistic, involving multiple gods and goddesses. Christianity was different in being monotheistic or believing in only one deity. Christianity was one of several religions introduced to Britain from the eastern part of the empire, others being those dedicated to certain deities, such as Cybele, Isis, and Mithras.
After the collapse of Roman imperial administration, much of southern and eastern Britain was affected by the Anglo-Saxon migrations and a transition to Anglo-Saxon paganism as the primary religion. The Anglo-Saxons were later converted to Christianity in the seventh century and the institutional church reintroduced, following the Augustinian mission. There remained an awareness among Anglo-Saxon Christian writers like Bede that a Romano-British Christianity had existed. In fact, the Romano-British church existed continuously in Wales.