High kings reigned in Ireland from the A.D. 200’s to the 1100’s. The title high king was a nominal one. It did not necessarily give a king authority over other kings.
In the A.D. 200’s, the legendary figure Cormac mac Airt is said to have reigned from Tara, in what is now County Meath, and called himself árd rí (high king). A succession of high kings maintained the superiority of Tara until the 560’s. One of the most important successors was Niall of the Nine Hostages (379-405). His descendants retained the high kingship for several hundred years.
King Brian Boru, who reigned from 1002 to 1014, was the most illustrious and powerful of the high kings. He defeated Danish invaders at the Battle of Clontarf—a turning point in Irish history. The last high king was Ruaidrí Ua Conchobair (Rory O’Connor), who died in 1198.