23 April in military history: Battle of Clontarf, 1014

By the traditional dating it was fought on Good Friday, 23 April 1014, at Clontarf, on Dublin Bay. The year is certain, but the earliest annals give neither the day nor the place. According to Seán Duffy, the day is given by the Cogadh Gáedhel re Gallaibh and by the chronicle of Marianus Scottus.

Brian Boru's army, mainly from Munster with some kingdoms of southern Connacht and Máel Sechnaill, king of Tara, fought the Norse of Dublin, the men of Leinster under their king Máel Mórda, and overseas allies under Sigurd, Earl of Orkney, and Brodir. Sitric Silkbeard, king of Dublin, reputedly stayed inside the town.

He probably did not fight in the battle himself. The Annals of Loch Cé say that a man fleeing the battle, whom they call a Danmarkian, beheaded him as he chanted psalms behind the battalions; the Cogadh, Njal's saga and a gloss in the Annals of Ulster make Brodir the killer, a role the historian Ailbhe Mac Shamhráin thinks probably fictional.

The annals differ. The Annals of Ulster count six thousand of the foreigners killed or drowned, and the Annals of the Four Masters at least three thousand slain. Brian, his son Murchad, his grandson Tairdelbach, Máel Mórda and Sigurd were among the dead.

Historians disagree. Donnchadh Ó Corráin argued that it was not a struggle between the Irish and the Norse for the sovereignty of Ireland, while Seán Duffy holds that Brian prevented a Viking takeover. Patrick Wallace agrees with Ó Corráin that the result did not break the power of the Norse forever.