Diarmait Ua Briain

Who was Diarmait Ua Briain?

Diarmait Ua Briain was an 11th-century Irish king who ruled Munster from 1114 to 1118.

One of three sons of Toirdelbach Ua Briain, he was banished from Munster by his brother Muirchertach Ua Briain shortly after the death of their father in 1086. He lived in exile for several years while his brother ruled as King of Munster. He is believed to have been the commander of the Irish fleet that supported Rhys ap Tewdwr at the Battle of Mynydd Carn.

In 1093, he reconciled with Muirchertach after recognizing his claim and was installed as dux of Waterford. He eventually succeeded his brother as acting King of Munster when his brother became seriously ill in 1114. After taking the throne, he banished Muircheartach and soon was involved in a four-year struggle for control of Munster. In 1116, he attacked Muirchertach and Brian Ua Briain "in violation of a mutual oath on the relics of Ireland" besieging Limerick. This resulted in Muirchertach making peace with Diarmait, however he was eventually captured by Muircheartach.

He later died in Cork in 1118 and in the same year, Toirdelbach Ua Conchobair invaded Munster and partitioned the land between the sons of Diarmait Ua Briain and Tadg Mac Carthaig, Conchobar Ua Briain of Thomond and Toirdelbach Mac Carthaig of Desmond respectively.