April 23, 1004: Irish Defeat Vikings at Battle of Clontarf

Brian Boru, the high king of Ireland, is assassinated by a group of retreating Norsemen shortly after his Irish forces defeated them.

Brian, a clan prince, seized the throne of the southern Irish state of Dal Cais from its Eogharacht rulers in 963. He subjugated all of Munster, extended his power over all of southern Ireland, and in 1002 became the high king of Ireland. Unlike previous high kings of Ireland, Brian resisted the rule of Ireland's Norse invaders, and after further conquests his rule was acknowledged across most of Ireland. As his power increased, relations with the Norsemen on the Irish coast grew increasingly strained. In 1013, Sitric, king of the Dublin Norse, formed an alliance against Brian, featuring Viking warriors from Ireland, the Hebrides, the Orkneys, and Iceland, as well as soldiers of Brian's native Irish enemies.

On April 23, 1014, Good Friday, forces under Brian's son Murchad met and annihilated the Viking coalition at the Battle of Clontarf, near Dublin. After the battle, a small group of Norsemen, flying from their defeat, stumbled on Brian's tent, overcame his bodyguards, and murdered the elderly king. Victory at Clontarf broke Norse power in Ireland forever, but Ireland largely fell into anarchy after the death of Brian.