The Battle of Clontarf 1014 is often seen as a simple victory for the Irish over the Vikings, marking the end of the Viking power in Ireland and the final defeat of the invader.

This is simply not true. Clontarf - which was actually fought roughly where Croke Park now is - was an important battle in Brian Boru's long-running attempt to create a single political and military authority in Ireland. He was aspiring to be a High King in the true sense of the term.

Brian's centralising ambitions met with resistance from provincial sub-kings. In order to deal with them, Brian permitted Viking Dublin a continuing degree of local autonomy. However, he was outbid by the King of Leinster who succeeded in enlisting Viking support in a provincial revolt against Brian. That's what the Battle of Clontarf was all about. Although Brian won the battle, he lost his life.

He also failed in his ambition to create a single political authority in Ireland, something that would not happen until Cromwell managed it 600 years later. Seán Duffy, one of Ireland's foremost medieval historians, gets behind the myths to tell the true story of this famous battle.