O'Brien and Bashir in their costumes for the program
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") {Boru is considered the founder of the Irish Clan O'Brien}