When did the Vikings arrive in Ireland?
History of Ireland (800–1169)
Eoin MacNeill identified the "oldest certain fact in the political history of Ireland" as the existence in late prehistory of a pentarchy, probably consisting of the cóiceda or "fifths" of the Ulaid (Ulster), the Connachta (Connacht), the Laigin (Leinster), Mumu (Munster) and Mide (Meath), although some accounts discount Mide and split Mumu in two.[7] This is not an accurate description of the political landscape c. 800,[8][note 2] but when discussing the political subdivisions of Ireland at this time, it is still useful to refer to this system; if Laigin and Mide are combined as Leinster, it roughly corresponds with the modern four provinces of Ireland.