The Oirghialla were closely related to the Uí Maine. Similarly Armagh diocese was given the Cenel Eogain kingdom of Telach Óe, because it was in the territory of the old Airgialla kingdom of Uí Tuirtre. They were the Laiginian allies of the North-Gaelic tribe of Uí Neill, which virtually monopolized the high-kingship of Ireland during the post-fifth century historical period. Among the Uí Máine dwelt the Sogain, a Cruithin (Pict) tribe, and the Dal naDruithne believed to be Tuatha De Danann Celts. The Oirghialla helped the Uí Neill effect the conquest of most of North Ireland from the Ulster Érainn, and later they settled a vast territory there including the counties of Louth, Armagh, Monaghan and Fermanagh, a territory which is called after them, Oriel- the traditional home of the Síl Daimini branch of Airgialla. Similarly Armagh diocese was given the Cenel Eogain kingdom of Telach Óe, because it was in the territory of the old Airgialla kingdom of Uí Tuirtre.
The Uí Chremthainn anciently inhabited the territory between Lough Erne and the River Blackwater, in what is now County Fermanagh and the north of County Monaghan. The chief branches of the Uí Chremthainn include the Clann Lugain, and also the O’Mulroonys or Moroneys and the O’Boylans. The O’Boylans (O Baoigheallain) were of the same stock as the O’Flanagans (O Flannagain) of northwest Fermanagh. The O’Boylans were, after the Anglo-Norman invasion, lords of all Oriel, a widespread territory stretching from Fermanagh to Louth. Later, in the thirteenth century, their power in Oriel was subdued by the MacMahons, and their territory was reduced to what is now the barony of Dartry in the west of County Monaghan, an area then known as Dartraighe.
The term Airgialla were a group of mainly unrelated dynastys, translated as 'those who give hostages', or 'hostages of gold' alluding to a subordinate status of the various groups inhabiting the area. The earliest reference to the Airgíalla occours in the Annals of Tigernach under the yeare 677, where the death of Dunchad mac Ultan, "Ri Oigriall", is noted. Contemporary writers, e.g. O'Rahilly and Byrne, suggest the three Collas are mere doublets of the three sons of Niall Noigiallach who conquered portions of early Ulster, their names being Eogan, Conall and Enda. The three sons of Eochaid Duibhlein and Aileach, a daughter of the King of Alba, all bore the name of Colla - Colla Uais, Colla Meann and Colla da Crich (Fochr?h). The designation Colla, meaning strong man, was "imposed on them for rebelling," their original names being Cairsall, Aodh and Muredach, respectively.
The three Collas went to Scotland to obtain the assistance of their kindred to place Colla Uais on the Irish throne, and with their help placed him there, but he was compelled to give way to a relative, Muredach Tirech, who had a better title to the sovereignty. The entry in the Annals of Ulster under the yeare 697 which lists Mael Fothataig mac Mael Dub as "Rex na nAirgialla" may indeed be genuine. Both Mael Fothatag and his son, Eochu Lemnae (died 704) is listed as one of the guarantors of the "Cáin Adomnáin" in 697. Thus it is believed that the Airgíalla were probably in existence as an entity by then, or certainly by the opening years of the 8th century.