Mac Lochlainn [Ua Lochlainn], Muirchertach (d. 1166), high-king of Ireland, was the son of Niall, son of Domnall Mac Lochlainn. He was king of the Cenél nEógain (whose land, Tír Eoghain, gave its name to modern Tyrone), and his provincekingdom extended from the plains in the vicinity of the primatial city of Armagh to the Inishowen peninsula in Donegal. The family took its surname from Muirchertach's great-great-grandfather, Lochlainn (d. 1023), who was in turn almost certainly the great-great-grandson of Domnall, son of Áed Findliath (d. 879), king of Ailech. Muirchertach succeeded to the kingship following the death of his uncle, Conchobar, in 1136. He defeated the petty kings of the northern Cenél nEógain in 1139 and 1142, though in the latter he was severely wounded and was deposed in the following year. In 1145 he recovered the kingship of Cenél nEógain with the aid of the Airgialla and Cenél Conaill. Having secured his position in Tír Eoghain he was victorious in battle against the east Ulster kingdom of Ulaid in 1147. In the following year he replaced the reigning king of Ulaid with a more acceptable kinsman and secured the hostages of Ulaid, Airgialla, and Cenél Conaill at an assembly at Armagh, a gesture of submission that made him the paramount king throughout the north of Ireland. In 1149 he reasserted control over Ulaid and led a cavalry march south to receive the hostages of Bréifne and Mide; he then went to Dublin to receive the submission of the Ostmen (its Hiberno-Scandinavian rulers) and the hostages of their overlord, Diarmait Mac Murchada of Leinster.
This success made Mac Lochlainn a contender for the high-kingship of Ireland, a position then occupied by the ageing Connacht king, Toirrdelbach Ua Conchobair. In 1150 Mac Lochlainn obtained the hostages of Connacht, divided Mide in three, and in the following year launched an invasion of Connacht, again obtaining hostages as a sign of his supremacy. In 1152 he and Ua Conchobair, having made peace, joined forces and again partitioned Mide. However, Muirchertach and Ua Conchobair soon found themselves at war again. In 1153 Mac Lochlainn routed the forces of Connacht led by Toirrdelbach's son, Ruaidrí, while in the following year the Connacht fleet scored only a limited success in a major naval encounter off the Inishowen coast, primarily because Muirchertach had assembled a fleet from Galloway, Kintyre, and Man in order to withstand it. Although his forces suffered losses, Muirchertach was now in a sufficiently strong position to parade his armies through Connacht and Bréifne, and when he reached Dublin the Ostmen proclaimed him as their king; he then granted them twelve hundred cows as tuarastal or wages, a sign of his overlordship. Implicitly, this deed secured him the high-kingship of Ireland, though his reign is generally dated from the death of Toirrdelbach Ua Conchobair in 1156.
Mac Lochlainn invaded Osraige in alliance with Diarmait Mac Murchada in 1156. A year later he was in Munster, which he repartitioned, and having laid siege to Limerick was granted its kingship by the Ostmen. It may have been in commemoration of this circuit of Ireland that the propagandist poem known as Móirthimchell Éirenn Uile was composed. His reign did not go unchallenged, however. Ruaidrí Ua Conchobair attacked Tír Eoghain in 1157 and 1158, and in the next year he and his allies, Ua Ruairc and Ua Briain, challenged Muirchertach to battle at Ardee, in Louth, but were severely routed. Mac Lochlainn then ravaged Bréifne, billeted his troops on Mide for a month, and raided Connacht; and in 1161, having taken the hostages of Bréifne, he accepted the formal submission of Ruaidrí Ua Conchobair and Diarmait Mac Murchada and was declared by the annals king of Ireland without opposition.
As king, Mac Lochlainn was a munificent benefactor of the church. The Book of Kells contains a document by which he granted the church of Ardbraccan in Mide freedom from the exactions of secular rulers. Gill Meic Liac, head of the church of Armagh, made a circuit of Tír Eoghain in 1150 and 1162 and received tribute. In the same year Muirchertach gave the abbot of Derry, Flaithbertach Ua Brolcháin, a gold ring and other gifts and allowed him too to make a circuit of Tír Eoghain. In 1162 both king and abbot began an extensive building programme in Derry, culminating in 1164 in the erection of a ninety-foot-long church. In this same year, Muirchertach joined with the archbishop of Armagh in opposing the appointment of Flaithbertach to the abbacy of Iona. He was present at the consecration of the Cistercian abbey of Mellifont in 1157, at which he not only granted to the monks cows and gold but lands in the kingdom of Mide. At about the same time he issued a charter to the Cistercian house of Newry, Down, in which he styled himself rex totius Hiberniae (King of all Ireland) and by which he made a grant of lands in the vicinity to this house too.
Mac Lochlainn sought something akin to territorial ownership of the lands he conquered. In 1163, Diarmait Ua Máel Sechlainn paid him 100 ounces of gold for the kingship of western Mide. When Muirchertach invaded Ulaid in 1165, not only did he temporarily banish its king, Eochaid Mac Duinn Sléibe, but gave away lands in the latter's kingdom to Donnchad Ua Cerbaill of Airgialla and the church of Saul, in Down. In the following year, however, he treacherously blinded Eochaid, which incident brought about his own downfall. Tír Eoghain was invaded by the forces of Airgialla and Bréifne and, in a battle in south Armagh, Muirchertach was slain and was buried in the mausoleum of the kings at Armagh (at which the churchmen of Derry took grave offence). His death greatly weakened the Mac Lochlainn family and ultimately paved the way for the restoration of the Uí Néill to power in Ulster. He was succeeded as high-king of Ireland by Ruaidrí Ua Conchobair of Connacht, and, because Muirchertach's demise left exposed his ally, Diarmait Mac Murchada, who was thereupon banished overseas, his death indirectly precipitated the Anglo-Norman invasion of Ireland.
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