Ua Briain, Muirchertach (c.1050–1119) was a son of Tairdelbach ua Briain (qv) (d. 1086) and a great-grandson of Brian Bórama (qv). His mother was Derbfhorgaill, daughter of Tadc Mac Gilla-Phátraic, king of Osraige. Among his wives were Derbfhorgaill, daughter of Lethlobar grandson of Laidcnén. She was mother to Muirchertach's son, Domnall, who was politically active during the final years of his father's reign but of whom little is heard after the latter's death. Domnall himself died in clericatu in Lismore in 1135. Muirchertach was also father to Mathgamain, who died at Lismore six years previously, never having been engaged in public life. Nonetheless, he left his mark through his descendants, who took the surname Mac Mathgamna, settling later in the region of Corco Baiscinn in west Clare.
In contrast with his sons, Muirchertach adopted an active role early in his father's career, being appointed governor of Dublin by Tairdelbach in 1075, though an expedition northwards under his leadership in that year was defeated. He had greater success nine years later in the battle of Móin Cruinneóige against one of his father's principal enemies, Donnchad Ua Ruairc, whose head he brought back to Limerick in triumph. Towards the end of Tairdelbach's reign, however, he may have been increasingly involved in southern affairs, Anthony Candon suggesting that he served as king of Munster, ri láim a athar (at his father's (right-) hand) (‘Barefaced effrontery’, 13). Be that as it may, on his father's death in 1086 he succeeded to the kingship along with his brother Tadc and half-brother Diarmait (qv) (d. 1118). His power was such, however, that he was able to banish Diarmait after Tadc's unexpected death the following month. It was scarcely an auspicious start and during the early part of his reign he faced frequent opposition from Tadc's sons, and from his remaining brother. Thus, in 1086 Diarmait marched against Muirchertach in support of the Leinster king, Donnchad (qv) son of Domnall Remur (qv), but was defeated at Ráith Étair near Dublin. At the head of a naval force, he plundered along the coast of Cork the following year, but again success was limited. Muirchertach's kinsmen finally accepted the inevitable: Tadc's sons came to terms with him in 1091 though the peace was not to last, while Diarmait entered into a more stable relationship with him two years later.
As Diarmait's early alliance with Leinster shows, the men of the east wished to use the opportunity presented by a power change in Munster to reassert their independence. In his dealings with them, however, Muirchertach proved himself to be very much his father's son, ensuring that the various factions within the Uí Chennselaig remained divided. Thus, when Donnchad son of Domnall Remur was defeated by a rival kinsman, Énnae, in 1088, the latter had the support of a force from south Munster, presumably acting at Muirchertach's behest. Donnchad was killed the following year, by Muirchertach himself, according to one source, by Conchobar Ua Conchobair Fháilge (qv), according to another. Yet Énnae's hour had not come, since Muirchertach immediately had him imprisoned, a fate which similarly befell the Munster ruler's sometime ally, Ua Conchobair Fháilge, in 1094.
His initial encounters with Connacht were less successful, confronted as he frequently was by the powerful partnership of the western leader, Ruaidrí na Saide Buide Ua Conchobair (qv), and Domnall Ua Máelshechlainn of Mide. Indeed in 1088, they were additionally supported by the northern ruler, Domnall Ua Lochlainn (qv), who marched into Munster, destroying Muirchertach's fort at Kincora. The Munster king sought revenge the following year, plundering the churches of Lough Ree. Ua Conchobair repulsed him and on his retreat to Athlone, Ua Máelshechlainn attacked. There was worse to come: Muirchertach's opponents next turned their ferocious attention to Cashel, one annalist pondering whether ‘they left a beast or a human being in all that space’ (Ann. Tig.). Ua Briain had no option but to submit. His subservience was not to last, and in 1090 and 1091 he marched to Lough Ree again and invaded Mide, only to have his home base attacked by the Connacht–Mide duo later that year. The following year, however, his luck turned: Ua Conchobair was blinded by a rival dynast, Ua Flaithbertaig, and Muirchertach quickly seized the opportunity to install Gilla-na-náem Ua hEidin in the kingship. The latter fell from favour and he too was imprisoned, the Munster king bestowing power on Domnall Ua Ruairc in 1095. In so doing, however, he was careful to preserve the south Connacht territories of Uí Fhiachrach Aidni and Uí Maine for himself. His authority in the west was increasingly secure.
At the demise of his western ally, Ua Máelshechlainn chose to submit, travelling to Limerick to do so in 1093. This did not suffice; Muirchertach deposed the Mide leader the following year, and may also have been implicated in his murder soon afterwards. Adopting the policy that had proved effective in Leinster, the Munster king appointed joint rulers in Mide: Conchobar Ua Máelshechlainn in the east, and his kinsman, Donnchad, in the west. This had the desired result of setting the two at war with one another, ensuring that Muirchertach retained the upper hand. About this time too, he consolidated his control over Dublin, which had been intermittent during the first eight years of his reign. Having conquered the city in 1089, he was ousted two years later by Gofraid Méránach (qv) but succeeded in banishing the Manx interloper in 1094. The latter was allied to Domnall Ua Lochlainn, king of Ailech, who was to prove Muirchertach's most persistent opponent. Having achieved large-scale dominion over the southern half of the country by this time, Ua Briain's main concern for the remainder of his active career, till illness struck in 1114, was to extend his authority into the north. The calibre of his northern counterpart was such that he signally failed to do so.
In truth, however, Muirchertach's advances were frequently halted not by Ua Lochlainn's military might but by the negotiating tactics of his ecclesiastical ally, the abbot of Armagh. Thus, on six separate occasions between 1097 and 1113 when the Munster king marched northwards, comarba Pátraic (the successor of St Patrick (qv)) intervened to make peace, while in 1105 he travelled to Dublin to meet them to the same end. In their relatively rare encounters on the battlefield, on the other hand, both were equally matched, Muirchertach emerging victorious in 1101, having demolished Domnall's fortress at Ailech, while the northern king was triumphant two years later at the battle of Mag Coba (near Dromore, Co. Down). Despite suffering heavy losses, Ua Briain was back in the north the following year, though he failed to make significant inroads into Ua Lochlainn's territory.
Whether Muirchertach was supported in the disastrous battle of Mag Coba by his newfound ally, Magnus Barelegs, is not clear. The Norse ruler had first journeyed to Ireland six years previously, concerned perhaps by the extension of the influence of the Munster king beyond Ireland into the Isles, as evidenced by the request of the inhabitants in the 1090s that Muirchertach send them a suitable leader. All changed in 1102 when Magnus and his Irish counterpart agreed a truce symbolised by the marriage of the Norse king's 9-year-old son, Sigurd, to the Munsterman's 5-year-old daughter, called ‘Bladmynja’ in the saga of Magnus Barelegs. According to this literary source, having overwintered together, the two kings marched northwards and gained many victories in battle. What is certain, however, is that Magnus was killed while in the north in 1103 by the Ulaid, allies of Muirchertach, which, as Seán Duffy has suggested, may indicate that the two rulers had experienced ‘a parting of the ways’ (‘Irishmen and Islesmen’, 113). About the same time, another of Muirchertach's daughters was married to Arnulf de Montgomery, brother of Robert de Bellême, earl of Shrewsbury, who sought the assistance of the Munster king in his rebellion against King Henry I. That Muirchertach was involved is indicated by a letter written by him to Anselm of Canterbury, in which he gives thanks to the archbishop for interceding with the king on behalf of his son-in-law. Moreover, King Henry's displeasure was such that he imposed a trade embargo with Ireland as a result of the betrayal, Ua Briain being sufficiently skilful, however, to negotiate its removal.
Muirchertach was thus a key player in the European politics of his day, as his frequent dealings with contemporary rulers serve to underline. Although the precise circumstances of the gift are not known, in 1105 King Edgar of Scotland presented him with a camel. Furthermore, a number of Welsh rulers had reason to be grateful to him for continuous support. These included Cadwgan ap Bleddyn, king of Powys, and his son, Owain, in their war against the earls of Chester and Shrewsbury (1098, 1099), while Owain sought refuge again with Muirchertach eleven years later. Similarly, the king of Deheubarth, Rhys ap Tewdwr, along with his son, Gruffudd, were offered protection by him, with Gruffudd remaining in Ireland till 1113.
It is in the ecclesiastical sphere, rather than the secular, however, that his connections with the outside world are most significant, since, following his father, he engaged in correspondence with Anselm and became the major Irish patron of Gregorian reform. Already in 1096, his reformist credentials were evident in his choice, along with his brother, Diarmait, of a Winchester monk, Máel-Ísu Ua hAinmire (qv), as bishop of Waterford. His interest in episcopal appointments continued and he was involved in the installation of Gilbert (qv) as bishop of Limerick in 1106, and of Cellach (qv) as bishop of Armagh in the same year. Of greater importance was his role at two pivotal reforming synods: at Cashel in 1101, where he granted the Rock, long associated with his Munster rivals, the Éoganachta, to the church, and at Ráith Bressail a decade later, where the diocesan organisation of the country based on the twin pillars of Cashel and Armagh was firmly laid down.
His deference towards the northern church, similarly evident in his meek acceptance of repeated interventions in his struggle with Ua Lochlainn by the abbot of Armagh, was born of political realism, dictated by his desire for legitimisation by the one true national Church, as Anthony Candon has remarked (‘Barefaced effrontery’, 23). The quest for justification also lies behind the production of propaganda works at his behest. Thus, ‘Cocad Gáedel re Gallaib’ (‘The war of the Gaídil against the Gaill’), a heroic biography of Muirchertach's great-grandfather, Brian Bórama, written in the first decade of the twelfth century when the powers of the Munster king were at their height, consciously portrays the eponymous ancestor of Uí Briain in his descendant's image, thereby vindicating the trajectory of the younger king's career. In the same way, by highlighting the pre-eminence of the Munster king, the roughly contemporary tract Lebor na Cert (The Book of Rights), is equally supportive of Muirchertach's national aspirations, and may have been composed for one of the reforming synods, as Candon most recently has claimed (‘Barefaced effrontery’).
In the end, however, neither pen nor sword sufficed, as Muirchertach fell ill in 1114, his hoped-for conquest of the north as elusive as ever. Indeed, Domnall Ua Lochlainn, along with the Munster king's increasingly powerful Connacht rival, Tairdelbach Ua Conchobair (qv), took the opportunity to inflict an immediate defeat on the Munstermen. Yet Muirchertach's greatest threat came from his own kinsmen: his brother, Diarmait, supported by his sons, banished him from Limerick to the monastery of Lismore. A temporary recovery in 1115 enabled the Munster ruler to regain power, imprisoning his sibling in the attempt. Diarmait rebelled again the following year, taking Domnall, son of Muirchertach, captive and expelling Muirchertach once more eastwards to Lismore. Diarmait's long-sought-for success was not to last and he died, perhaps unexpectedly, in 1118. Muirchertach was nominally in control again, but a shadow of his former self, his power having all but disappeared. Nonetheless, on his death the following year he is rightly accorded the title rí Érenn (king of Ireland) and described as tuir ordain ocus airechais iarthair in domain (the tower of the honour and dignity of the western world) in the Annals of Ulster.
That Muirchertach's once imposing authority was far from secure is indicated by the speed with which it dissipated in the years following his illness, and by the much reduced kingdom inherited on his death by his successors, the three sons of his brother, Diarmait. His failure to transform personal gains into more permanent advances has rightly been criticised by commentators, but the political reorganisation this would have entailed was still some considerable way off. Nonetheless, he was concerned with institutional matters, greatly increasing the administrative trappings of his principal royal court at Limerick, where a succession of powerful rulers was forced to submit. In addition, he surrounded himself in Munster with key advisers, many of whom, including the Mide cleric, Máel-Muire Ua Dúnáin (qv), had been attracted southwards by Muirchertach's pre-eminence and modernising outlook. Yet he also took care to have recourse to tradition, frequently portraying his gains as the natural extension of that belonging by right to illustrious predecessors, in particular Brian Bórama. Moreover, he was acutely conscious of the importance of Armagh, Ireland's primatial church, seeing its secular equivalent in the national kingship he dearly wished to create. In the end, all-Ireland dominion was not to be his, though his control over Munster, Leinster, Mide, and Connacht remained firm, not least because of his ruthlessness in keeping rival kingdoms divided. It was a lesson well observed by his opponents, including Tairdelbach Ua Conchobair, whom Muirchertach had set up as king in 1106, at the expense of a more powerful claimant. When the southern king faltered a decade or so later, it was the young Connacht king who stepped into the breach, partitioning Munster into Desmumu (Desmond) under the Meic Carthaig in the south, and Tuadmumu (Thomond) in the hands of Uí Briain in the north. The latter's era was well and truly at an end, while that of Connacht was about to begin.