Clontarf Castle, Near Dublin The Clontarf area of Dublin holds a particularly important place in Irish history, thanks to the epic Battle of Clontarf in 1014 when Brian Boru, the High King of Ireland, defeated Mael Morda, King of Leinster. After the battle, Boru was later killed on what is now the site of Clontarf Castle. Hugh de Lacy, Lord of Meath, built the castle in 1172 as a form of protection for Dublin. The structure was rebuilt in 1837. In 1998, it reopened as a four-star hotel.