ABSTRACT
The O’Briens (Uí Briain) are descended from Brian Boru, king of the Dál Cais from 976. The Dál Cais, previously known as the Déisi Tuaiscirt until around 934, rose to prominence in the course of the ninth century. They expanded across modern County Clare and, in the second half of the tenth century, imposed their authority over the Viking town of Limerick. Compared with other dynasties in Munster, the Dál Cais were more dynamic and ruthless and tended to take direct possession of their neighbors’ lands rather than content themselves with mere overlordship.
