UA BRIAIN (UI BRIAIN, O’BRIEN) (Medieval Ireland)

The O’Briens (Ui Briain) are descended from Brian Boru, king of the Dal Cais from 976. The Dal Cais, previously known as the Deisi 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 Dal 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 Eoganachta to become king of Munster, with support from the Vikings of Waterford, and he asserted his authority over Leinster. He forced Mael Sechnaill II of the Ui Neill 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 Ui Neill 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, Mael Morda 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 grandiose, but Brian Boru had succeeded in breaking the Ui Neill 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 ("descendant 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 Raith Bressail (1111), which sought to transform the Irish church along Roman lines. Muirchertach may also have commissioned one of the most effective pieces of propaganda 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 resonated 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 Ui Briain kingdom of Thomond in northern Munster and a Meic Carthaig kingdom of Desmond in southern Munster. Tairrdelbach Ua Conchobair kept Munster divided to undermine the Ui 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 Ui Briain heartland of Clare to Connacht, driving them to accept Cormac Mac Carthaig, king of Desmond, as the king of Munster. Mac Carthaig led a coalition of forces from across the south of Ireland in a prolonged and savage war to overthrow Ua Conchobair’s hegemony. However, once the threat from Connacht was ended in 1133 the Uf Briain ended their alliance with Mac Carthaig, and Munster was split in two again. In 1138, Tairrdelbach Ua Briain, king of Thomond, succeeded in having Cormac Mac Carthaig assassinated. Thereafter he ruled all of Munster until 1151 when another rebellion assisted by Tairrdelbach Ua Conchobair, king of Connacht, this one led by Cormac Mac Carthaig’s son Diarmait, resulted in the province being partitioned again. The kings of Thomond and Desmond each looked upon the other as a deadly rival for the kingship of Munster.

In 1168, Diarmait Mac Carthaig, king of Desmond, had Tairrdelbach Ua Briain assassinated in an attempt to unite Munster under his authority. His ambitions, however, were thwarted by Ruaidrf Ua Conchobair, king of Connacht and high king of Ireland, who preferred to see Munster remain divided and easier to overawe. Ua Conchobair obliged Mac Carthaig to pay an eraic ("compensation") for the killing. Mac Carthaig’s assault on Limerick, the capital of Thomond, early in 1171 failed to advance his aspirations for the kingship of Munster for the same reason. Indeed, Domnall Mor Ua Briain, king of Thomond, had aspirations of his own for the kingship of Munster, and he formed an alliance with Ua Mathgamna (O’Mahony), one of Mac Carthaig’s chief subordinates, in a plan to invade Desmond in October 1171. Coincidentally, Henry II, king of England, had just landed in Ireland in order to assert his authority over some Anglo-Norman adventurers (they knew themselves simply as "English") led by Richard de Clare, earl of Pembroke, better known as Strongbow. Mac Carthaig submitted to Henry II in a bid to avoid the planned Ua Briain invasion, prompting Domnall Ua Briain and Ua Mathgamna to do likewise. Impressed by the alacrity with which the kings in Ireland were willing to submit to him, Henry II decided to revive the papal grant of Ireland to him in the privilege known as Laudabiliter.

Anglo-Norman Invasion

Limerick was captured by Anglo-Norman or English adventurers in 1175, but its occupation was short-lived. In 1177, Henry II granted the Ua Briain kingdom of Thomond and the Mac Carthaig kingdom of Desmond to three of his leading knights. Domnall Ua Brian managed to repulse Philip de Braose, the grantee of Thomond, at the walls of Limerick and save Thomond from invasion. By contrast, the unwalled town of Cork fell easy prey to its grantees and became the center of a new English colony in southern Ireland. Ua Briain took advantage of Mac Carthaig’s discomfiture by invading Desmond late in 1177. Ua Briain’s efforts failed, but they were instrumental in forcing Mac Carthaig to temporize with the English and concede a large part of his kingdom to them.

Domnall Ua Briain’s strategy in dealing with the English thereafter was to continue to offer robust resistance while showing a willingness, nonetheless, to reach an accommodation with the English crown in order to safeguard as much as possible of his kingdom. When the Lord John came to Ireland in 1185, Ua Briain, together with Ruaidrf Ua Conchobair of Connacht and Diarmait Mac Carthaig of Desmond, submitted to the prince, but the Irish kings were treated with open contempt and derision. John granted northeastern Thomond to Theobald fitz Walter, ancestor of the future Butler earls of Ormond, and he granted much of southeastern Thomond to Philip of Worcester and William de Burgh. Ua Briain offered stout resistance to the invaders, and it was only following his death in 1194 that the English were able to consolidate their control of Ormond and capture the capital of Thomond, Limerick. John granted Limerick the status of a royal borough around 1197, and he gave away much of the Ua Briain lands in Limerick diocese to the sons of Maurice fitz Gerald, ancestor of the future earls of Desmond.

Donnchad Cairbrech Ua Briain (c. 1242), the next strong king of Thomond, concentrated his efforts on safeguarding the Uf Briain heartland in Clare from English incursions. He reached an accommodation with King John wherein he accepted a knighthood and committed himself to paying a substantial rent to the English crown for his diminished kingdom. It was a strategy that largely succeeded, though there were lesser Uf Briain who dissented from his policy of collaboration with the English.

Conchobar, Donnchad’s son and successor, continued his father’s strategy, but from 1248 Henry III, king of England, made grants resulting in English colonization in and around Bunratty. When the English sought to make further inroads into Thomond, Conchobar fought back hard and routed an English force sent against him in 1257. In the following year his son Tadc Ua Briain met with Aed Ua Conchobair, king of Connacht, and Brian Ua Neill, king of the Irish of Ulster, at Cael Uisce to agree to the formation of a national confederacy against the English. The confederation proved to be short-lived, however. Tadc died in 1259, and Ua Neill was killed soon afterward. The Irish were too divided among themselves, and too weak in any case, to mount an effective nationwide resistance to the English. Nonetheless, Ua Briain hostility toward the colonists in Thomond continued unabated, and there was widespread devastation in the borderlands around Bunratty and Limerick.

In a bid to overcome the determined opposition of Ua Briain, Edward I granted all of the Ua Briain lordship to Thomas de Clare, brother to the king’s chief adviser, the earl of Gloucester. De Clare made some kind of agreement with Brian Ruad Ua Briain, the king of Thomond, but treacherously killed Ua Briain in 1277. Brian Ruad’s sons prevented de Clare from taking immediate advantage of their father’s murder. However, Thomond was without a strong leader, and internecine rivalry among the Ui Briain allowed de Clare to force the next king of Thomond, Tairrdelbach Ua Briain, into an arrangement whereby he agreed to hold all of Thomond beyond Bunratty for an annual rent of £120. Following his death, there was further internecine strife among the Ui Briain which was exploited by Richard de Clare. De Clare sought to extend his sway across County Clare, but at the battle at Dysert O’Dea in 1317 de Clare was killed by forces led by Muirchertach Ua Briain, a son of Tairrdelbach Ua Briain. The threat from the de Clares was ended and the Ui Briain’s control of Thomond was assured. The battle at Dysert proved to be a decisive encounter.

The Ui Briain Revival

After Dysert O’Dea, the Ui Briain went on the offensive against the English colonists. The colony at Bunratty was put under sustained pressure and fell to the Irish in the 1350s. The frontiers of O Briain power were pushed right up to the walls of Limerick. There were repeated raids east of the Shannon to harass the English lordships in Ormond. In 1370, Brian Sreamhach Ua Briain, king of Thomond, won a great victory against the earl of Desmond south of the Shannon. His subordinates captured and sacked the city of Limerick. Such audacity, however, prompted the intervention of the English chief governor, Sir William de Windsor, and an uneasy modus vivendi was established between Ua Briain and the embattled English colonists. Limerick was restored to English control, but Ua Briain was in the ascendant.

In 1466, Tadc Ua Briain, lord of Thomond, led an army across the Shannon and imposed his overlord-ship over the MacBriens of Coonagh and Aherlow and the Clanwilliam Burkes. He imposed a "black rent" on the inhabitants of Limerick city and the east of County Limerick, a financial tribute reflecting his military power. At the close of the Middle Ages, the Ui Briain were again one of the most powerful dynasties in Ireland.


It has to be conceded that the Ui Briain were fortunate in that their heartlands, in modern County Clare, were relatively remote from England and accordingly less attractive to English colonists. Also, their core territory had the advantage of geographical cohesion, bounded as it was by the Shannon river and estuary, the Atlantic Ocean, and the lordship of the Gaelicized Clanrickard Burkes with whom they maintained good relations. Nonetheless, the survival of the O Briain lordship in the later Middle Ages was due primarily to the tenacity and resourcefulness of its leaders. Their grasp of real-politik, and their readiness to seek and maintain accommodations with the English while offering stiff resistance to incursions west of the Shannon, helped them to come through the most threatening phase of English colonization up to 1317. Their firm governance and control of their subordinates within Thomond gave them the strength to take advantage of English weaknesses subsequently so that they became a force to be reckoned with across much of the territory of the former kingdom of Thomond. That strength and adaptability was demonstrated again in 1542 when Muirchertach Ua Briain became the first earl of Thomond under the auspices of Henry VIII’s policy known as "surrender and regrant." The earldom was a recognition of Ua Briain’s stature as one of the most important lords in Ireland.

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