The Age of Saints
The Christian church had an uncertain start in Britain. During the Roman occupation Christianity was but one of several popular cults. After Constantine the Great proclaimed Christianity the official religion of the Roman Empire in 313, it flourished - or at least, more people paid lip service to it.
After the departure of the Romans from Wales in the late 4th century, Christianity, which had been primarily a religion of the Romanised upper classes, suffered. There is even some suggestion that it died away completely. If that is the case, it was due for a startling resurrection, led by a few major figures in south-east Wales.
The first of these "saints" of Celtic Christianity was Dyfrig (Saint Dubricius), a bishop at Ariconium in the kingdom of Erdig. Dyfrig probably lived from about 425-505AD.
Dyfrig was heir to the Roman tradition of Christianity, and may well have been a disciple of Germanus of Auxerre. The details of Dyfrig's life are scanty; more important is the knowledge that through him and his followers the Christian tradition was kept alive at a time when paganism was in ascendance in Britain.
After Dyfrig's death his position as leader of Christian Wales was taken by Illtud. Unlike Dyfrig, Illtud was an abbot, not a bishop. This in itself is interesting, for it shows that the monastic lifestyle had taken root in Wales.
Illtud's fame, however, rests on his scholarship; he was abbot of the monastic school at Llanilltyd Fawr (Llantwit Major in Glamorgan). At this early stage of monasticism in Wales, monks had not yet adopted the severely ascetic, isolated life that they would later embrace. So Illtud's school at Llantwit Major drew scholars from across the Celtic world, from Ireland, Brittany, and Cornwall.
These scholars included the monk Gildas, whose later work "De Excidio Britanniae" (Concerning the Fall of Britain) is one of the best (read one of the few) written records we have of this early period of Welsh and English history.
Illtud himself was later inter-twined with the legends of King Arthur. Some tales had him being one of the three knights entrusted by Arthur with the Holy Grail. Others state that Illtud was Sir Galahad. These tales are interesting not so much for their factual basis (dubious at best), but for the way in which the "heroes" of Welsh Christianity were merged with tales of secular heroes like Arthur and his knights.
Many of the monks who would later spread Christianity to Ireland were educated in Wales at this and other monastic schools. Over the course of the early 6th century the scholarly impetus lost ground to the ascetic impulse; monks left organised communities and settled in isolated areas to lead extremely simple lives of prayer and personal communion with God. This is the true "Age of Saints" in Wales. The Welsh saints were often not concerned with spreading the Christian message to the masses, but in retreating from society as far as possible.
Christian communities did spring up. These llannau - basically a consecrated enclosure for burying Christian dead - were frequently dedicated to the patron who granted land, though this does not explain the large number of llannau dedicated to Christian leaders like Dewi (David) or Teilo.