As I undestand it, according to British myth the excuse for them
being so weak that they had to invite in the Saxons was that thier
manpower was depleated by the "three great levies" - one was Magnus
Maximus' invasion of europe in 380-ish, one was led by "Erp the Pict"
around the same time (as Drust macErp was King of the Picts around
450-ish), and one was to Ireland. Problem is I can't find even a hint
of Romano-British involvement in Ireland anywhere close to this time.
Does anybody have any idea what/when/why the Irish invasion
would have been about???