Fosterage in the Annals of the Four Masters: The Case of Diarmait mac Máel na mBó and Tairdelbach Ua Briain

This article examines the evidence for a specific instance of fosterage in the eleventh century: an item in the Annals of the Four Masters which claims that Tairdelbach Ua Briain, king of Munster, was the foster-son of Diarmait mac Máel na mBó, king of Leinster. The timing and possible circumstances for this arrangement will be considered. It is argued that the later association between Tairdelbach and Diarmait has made scholars more accepting of a potential fosterage relationship. This discussion has wider implications for the study of fosterage in medieval Ireland, particularly in a political and dynastic context.