The three centuries that followed the fall of the Western Roman Empire were in many respects seminal for the emergence of western Europe. In no area was this more true than in that of religion. By the early fifth century the Empire was theoretically Christian. That is not to deny the existence of pagans within its boundaries: there were many, and they were to be found at all levels of society. There were still pagan intellectuals among the upper classes, and there were also plenty of more ordinary folk – especially among the lower classes of the countryside, but also among those who lived in the cities, including Rome itself – who continued to perform rituals which were condemned as idolatrous by the church. Nevertheless, from the fourth century onwards Christianity was the religion of the emperor and of the state, and the church was well established. It had numerous places of worship, especially in the towns; it was endowed with vast estates and a considerable amount of revenue, and it had a hierarchy of officials. Its leading clergy legislated on doctrine and on Christian behaviour in numerous councils, and they were among the most influential figures within the Empire.

The barbarian invasions upset, but did not destroy, this state of affairs. In some peripheral areas the church suffered considerably. In Britain, after the Saxon invasions, its survival was confined largely to the west, although there were Christian communities further east, whose existence is chiefly attested by place-names, but can also be inferred from the survival of such cults as those of Alban and Sixtus. In the provinces of Germania and Belgica some dioceses experienced considerable disruption: in one or two instances episcopal appointments appear not to have been kept up, and some ecclesiastical organisation may consequently have collapsed, only to be restored one or two centuries later in a period of growing pastoral enthusiasm.