406–409 and after

The Roman withdrawal from Britain and the Anglo-Saxon conquest

By 406 no Roman legions remained in Britain, and in 409 Emperor Honorius told the Britons they must defend themselves.

From the mid-5th century the Angles, Saxons and Jutes pushed the Celts to the west of the island and into Brittany. Since the Celts made little effort to convert their conquerors, Christianity in eastern Britain largely disappeared.

Cut off from the continent, Celtic Christianity developed its own customs. Notable among them were private confession (penitentials) and an 84-year Easter cycle, while Rome adopted a 19-year cycle from 455. This divergence fed later disputes (e.g. the Synod of Whitby).