Battle of Clontarf
From Memory Alpha, the free Star Trek reference.
The Battle of Clontarf was an engagement that took place in Ireland in 1014. High King Brian Boru lead his warriors against the invading Vikings, although he himself was killed during the battle. This battle ended the power of the Vikings in Ireland.
Miles O'Brien, who claimed to be a descendant of Boru, created an holoprogram of the battle and enjoyed reliving the battle in Deep Space 9's holosuites. (DS9: "Bar Association", "It's Only a Paper Moon")
