The origins of Christian Ireland are mysterious. When St. Patrick reached Auxerre in 415 AD, he found an Irishman among the clerics of Saint Amator. Thus, there is evidence that there were Irish Christians before St. Patrick‘s arrival, who were perhaps converted by slaves captured on the British coast. Records exist of five pre-Patrician bishops of Irish birth. Given the extensive trading between Ireland and the continent, it is probable that Irish merchants, travellers and traders would also have been familiar with Christianity.
The history of Christianity in Ireland dates from Palladius. During the early 5th century, the Pelagian heresy was disintegrating. At the request of the Deacon Palladius, Pope Celestine sent Germanus, Bishop of Auxerre, to re-convert the British heretics (Germanus later consecrated St. Patrick Bishop of Ireland). Christianity was established in Britain through a gradual process of cultural assimilation, rather than substitution. Similarly, in Ireland Gaelic culture remained largely unchanged, despite widespread conversion. The new faith was successfully filtered through the existing culture, language, and political system.
In western Europe, the Christian Church tended to mirror the organisational model of the Roman Empire. As the Roman Governor ruled over a province and lived in the town, so the bishop ruled over a diocese and also lived in the town. Christianity was easily introduced into regions previously conquered by the Romans. Since Ireland was never Romanised, it was quite difficult to reproduce the same kind of organisational structure. The fragmented political structure of Gaelic society compounded matters further. The introduction of Christianity into Ireland was not an organised endeavour. Monasticism had always been an aspect of Christianity and it spread rapidly to western Europe under the influence of hermits in Egypt such as Paul and Anthony. In Ireland, monasteries were the predominant form of Christianity because they did not require urban centres and thus were easily adapted to rural Gaelic society.
Life was difficult in these early monastic communities. The daily rituals associated with ascetic piety, such as reciting the psalter immersed in icy water, or praying for long hours with the arms held out in the forms of a cross, were arduous. Perhaps not all Irish monks favoured such extreme forms of penance and prayer, but yet, they did submit to a penitential regime which now seems astounding. These men sought expiation, in cells lost in the midst of the woods or on barren hillsides; the finest examples of a well tried faith were forged there. In order to standardise these customs, the leaders of the early Irish church wrote the Penitentials, special treatises, or catalogues of sins accompanied by the necessary acts of expiation. Even today, the Penitentials are infamous for their severity. This Irish practice of penance was a notable contribution to the Church and to Christianity.