Dál Cais

Dál Cais, a dynasty which was the dominant force in Munster for much of the 10th, 11th, and 12th centuries, producing a number of claimants to the high kingship. In the 11th century they adopted the surname Uí Briain after their most famous son, Brian Bóruma (Boru).

Of humble beginnings, the Dál Cais were originally known as In Déis Tuaiscirt who, having lost their lands south of the Shannon in Co. Limerick, sought to gain a foothold in Clare in the early 8th century. At this period, a number of individual groups within Dál Cais were vying for position but about the beginning of the 10th century the Uí Thoirdelbaig emerged victorious, though it was a member of the Uí Óengusso, Rebachán mac Mothlai, who was first termed ‘king of Dál Cais’ on his death in 934.

The change of name to ‘Seed of Cas’ indicates considerable political ambition: by linking themselves to Cormac Cas, supposed son of Ailill Ólum and brother of Eógan Mór, ancestor of the Eóganacht, this hitherto unknown group was staking a claim to the kingship of Cashel. That claim, however, could only be realized by military might and political supremacy, and it was under the rule of Cennétig, son of Lorcán (d. 951), and, more particularly, under that of his sons, Mathgamain and Brian Bóruma, that the Dál Cais rose to political dominance, aided by a corresponding decline in Eóganacht fortunes. A succession of able rulers among Brian Bóruma's descendants ensured that the Dál Cais were able to maintain that position more or less down to the early 12th century.

Ever mindful of their humble origins, however, they marked their period in power by the production of a number of literary works which sought to validate their new‐found political supremacy. Thus, their genealogies claimed for them an equal alternate right, shared with the Eóganacht, to the kingship of Cashel, while entries reflecting well upon them were inserted retrospectively into the Annals of Inisfallen. Eleventh‐ and 12th‐century pseudo‐historical compositions such as Lebor na Cert and Cogadh Gaedhel re Gallaibh were designed to glorify them further. Dál Cais days of glory began to come to an end, however, in the latter years of the reign of Brian Bóruma's great‐grandson Muirchertach Ua Briain (d. 1119). Therafter, the Uí Briain appear merely as one of a number of skilful players on the Munster political scene.

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