The later constricted kingdom of Airgíalla survived in Monaghan—which was known as Oirghialla and Oriel after the Norman Invasion of Ireland—under the Mac Mathghamhna, until the end of the Gaelic order in Ireland.

[citation needed] After the Anglo-Norman invasion, the anglicisation Uriel became the name of the part of Airgíalla that had extended into modern-day County Louth.

In the beginning of the 4th century, three warlike brothers, known as the Three Collas, made a conquest of a great part of Ulster, which they wrested from the Ulaid.

However, in general it can be shown that the origin legend was written (or composed) in the second quarter of the 8th century to seal their alliance with the Northern Uí Néill.

[attribution needed] The earliest reference to the Airgíalla occurs in the Annals of Tigernach under the year 677, where the death of Dunchad mac Ultan, "Rí Oigriall", is noted.

Rossa Buidhe had ascended to the Airgíalla kingship in 1579 and found himself geopolitically in an undesirable position; wedged between an expanding Tudor kingdom and Tír Eoghain under the O'Neill.

Initially, Rossa Boy made moves which suggested an alliance with Tír Eoghain, as he married the daughter of Hugh O'Neill, Earl of Tyrone.

Brian Mac Hugh Og was then the tanist to the chieftainship of his people according to the native Brehon laws and O'Neill was hoping to bring the "phantom" Airgíalla realm back into his camp on the death of Rossa Buidhe through this pact.

As a consequence, a military force led by Henry Bagenal was sent into the county in early 1589 to impose the sheriff and by the summer of that year, Rossa Boy was dead[how?].