U

UA BRIAIN (UÍ BRIAIN, O’BRIEN)
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. Com-
pared 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.

High Kingship

Brian Boru displaced the Eóganachta to become king
of Munster, with support from the Vikings of Water-
ford, and he asserted his authority over Leinster. He
forced Máel Sechnaill II of the Uí Néill to relinquish
his claim to overlordship of the south of Ireland. Brian
Boru showed determination in harnessing the wealth
of Munster and in projecting the inherent demographic
and economic power of the province over the rest of
Ireland. In 1001, Brian Boru attacked the Uí Néill and
subsequently established himself as the high king of
Ireland. On Good Friday 1014, Brian and his allies,
including Vikings from the southern towns, fought a
rebellious king of Leinster, Máel Mórda and his Viking
allies from Dublin, at Clontarf. Brian Boru was
killed in battle, as was the king of Leinster. Brian
was buried at Armagh, Ireland’s premier church. The
Book of Armagh
called him the
imperator Scottorum
(“emperor of the Irish”). That title was a little grandi-
ose, but Brian Boru had succeeded in breaking the
Uí Néill monopoly of the high kingship of Ireland and
made himself the king of Ireland. It is not surprising that
his descendants called themselves Ua Briain (“descen-
dant of,” literally “grandson of”) after him.

Brian Boru’s son and successor, Donnchadh (

c.

1064),

was unable to maintain his father’s hold on the high

kingship. However, Tairrdelbach Ua Briain, a nephew

of Donnchadh’s, succeeded in making himself “king

of Ireland with opposition” between 1072 and 1086,

meaning that his authority was recognized throughout

most but not quite all of Ireland. Tairrdelbach’s son,

Muirchertach Ua Briain, went further, ruling as king

of Ireland from 1088 until 1118 and coming close to

establishing a true Irish monarchy. Muirchertach is

strongly associated with the twelfth century church

reforms, and particularly with the synod of Cashel I

(1101) and the more important synod at Ráith Bressail

(1111), which sought to transform the Irish church

along Roman lines. Muirchertach may also have com-

missioned one of the most effective pieces of propa-

ganda produced in medieval Ireland—

Cogadh Gaedheal

re Gallaibh

(“The war between the Irish and the

Foreigners”). The

Cogadh

, written circa 1109–1118,

glorified Brian Boru as the national savior of the Irish

from the Viking onslaught at the Battle of Clontarf.

It made Brian Boru a legend and created a myth of

national resistance to foreign oppression that reso-

nated among Irish nationalists well into the twentieth

century.

Partition of Munster

A rebellion by the MacCarthys in southern Munster in

1118, backed by Tairrdelbach Ua Conchobair, king of

Connacht, resulted in the division of Munster in two:

an Uí Briain kingdom of Thomond in northern Munster

and a Meic Cárthaig kingdom of Desmond in southern

Munster. Tairrdelbach Ua Conchobair kept Munster

divided to undermine the Uí Briain and preempt any

challenge they might attempt to his aspirations to

becoming the king of Ireland. It seems that in the late

1120s Ua Conchobair annexed the Uí Briain heartland