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DÁL CAIS
Dál Cais was the name of the Munster people based
in eastern County Clare that rose to prominence in the
latter half of the tenth century and produced a number
of powerful kings, including Brian Boru. Although
they claimed kinship with the Eóganachta, who had
dominated the province since the dawn of history, the
Dál Cáis actually belonged to the larger population of
Munster Déisi, who were ethnically Érainn. This Déisi
population originally formed a loose conglomerate
stretching from southern Waterford into Limerick, but
by the eighth century, they had divided into two separate
groups—the Déisi Muman of Waterford and southern
Tipperary, and the western Déisi of Limerick. In the
latter territory were the Déis Deiscirt, who were even-
tually eclipsed by their neighbors, and the Déis Tuais-
cirt, who later changed their name to Dál Cais.
Although legend has it that they conquered their lands
in eastern County Clare from Connacht in the fifth cen-
tury, historical sources suggest that they did not actually
gain possession of this territory until the early eighth.
It is not known exactly when the Déis Tuaiscirt
adopted the name Dál Cais, but it is first used of them
in the Annals of Inisfallenunder the year 934, in an
entry recording the obit of their king, Rebachán mac
Mothlai. His death is also important for marking a
major transition in internal Dál Cais politics. For some
time prior, the kingship had been controlled by
Rebachán’s sept, the Clann Óengusso, but at his death,
the office was seized for the first time by their rivals,
the Uí Thairdelbaig. Under this new leadership, the
Dál Cais began a program of expansion that would
soon make them one of the most powerful kingdoms
in Ireland.
This expansion began in earnest with the rule of
Cennétig mac Lorcáin, who had extended his sway
over much of north Munster by the time of his death
in 951. Building on his father’s success, Mathgamain

mac Cennétig extended Dál Cais rule even further by

seizing the kingship of Cashel and thus putting an end

to centuries of Eóganacht rule in Munster. More impor-

tantly, though, Mathgamain also gained control of the

Norse settlements of Waterford and Limerick, the

resources of which were needed to sustain Dál Cais

expansion. In 976, Mathgamain was succeeded by his

brother, Brian Boru, who went on to become the most

powerful king in Ireland. However, the deaths of Brian

and a number of his important kinsmen at the Battle

of Clontarf in 1014 crippled Dál Cais. By the time they

reemerged in the late eleventh century, the ruling fam-

ily of Uí Thairdelbaig had adopted the surname Ua

Briain (O’Brien), and they enjoyed a considerable

revival under Tairrdelbach (d. 1086) and, later,

Muirchertach Ua Briain. But with the latter’s death in

1119, the days of the great Dál Cais kings came to an

end. After the Anglo-Norman Invasion, the O’Briens

were essentially restricted to their lands in Thomond,

where they retained some power throughout the later

Middle Ages.

DANM. WILEY

References and Further Reading

Byrne, Francis John. Irish Kings and High-Kings, 2nd ed. Dub-

lin: Four Courts Press, 2001.

Ó Corráin, Donncha. Ireland before the Normans. Dublin: Gill

and Macmillan Ltd, 1972.

Ó Cróinín, Dáibhí. Early Medieval Ireland 400–1200. New

York: Longman Group Ltd, 1995.

See alsoBrian Boru; Déisi; Eóganachta; Érainn;

Munster; Ó Briain; Ua Briain, Muirchertach; Ua

Briain, Tairrdelbach

DANCE

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