Airgíalla (Old Irish pronunciation: [ˈœɾʲɣʲiːa̯l̪a]; Modern Irish: Oirialla, English: Oriel, Latin: Ergallia) was a medieval Irish over-kingdom and the collective name for the confederation of tribes that formed it. The confederation consisted of nine minor kingdoms, all independent of each other but paying nominal suzerainty to an overking, usually from the most powerful dynasty. Airgíalla at its peak roughly matched the modern dioceses of Armagh and Clogher, spanning parts of counties Armagh, Monaghan, Louth, Fermanagh, Tyrone and Londonderry. Its main towns were Armagh and Clogher. The name's usage survives as a cultural area of folk tradition in South East Ulster and adjoining areas of County Louth.
According to legend, Airgíalla was founded by the Three Collas, who are said to have conquered what is now central Ulster from the Ulaid. The decisive victory was the battle of Achadh Leithdheirg, said to have been fought around the year 331. However, this tale is thought to be mostly fiction, and the actual year and circumstances of how the Airgíalla confederation came about is unknown.
