Roman calendar dating
Each had to be converted separately and each had to have its own Church structure, with priests and bishops effectively replacing the druids.
Eventually five provincial kingdoms arose in the place of this hotchpotch of petty rulers: Munster in the south of the island, Leinster and Meath in the east, Connaught in the west, and Ulster in the north.
Like many future, Irish monasteries, Lérins was situated on a small island.
A major divergence between Ireland and Rome lay in the former's older, and actually incorrect, method of calculating the date of Easter, in which the Irish Church used a 84-year cycle based on the lunar calendar.
On the odd occasion, such as the reign of Brian Boru (1002-1014), one of the provincial kings would claim the high kingship over all Ireland, based at the ancient site of Tara in County Meath.
This high kingship was never uncontested or of any lasting significance.
At the top were the druids, bards, lawmen and doctors, while the slaves at the base of the system had no rights.
As remarked by historian David Ross, the concept of territorial dioceses could not function in such a social system.