F. Haverfield, The Romanization of Roman Britain
“ The Celtic revival was due to many influences. We may find one cause for it in the Celtic environment of the province. After 407 the Romanized area was cut off from Rome. Its nearest neighbours were now the less-Romanized Britons of districts like Cornwall and the foreign Celts of Ireland and the north. These were weighty influences in favour of a Celtic revival. And they were all the more potent because, in or even before the period under discussion, the opening of the fifth century, a Celtic migration seems to have set in from the Irish coasts. ”
