Diarmait Mac Murchada (b. 1110; d. Ferns, 1171), king of Leinster, was famous as the king who appealed for military aid to King Henry II of England (1154-1189) and thereby precipitated the Anglo-Norman invasion.

Mac Murchada is certainly one of the most maligned historical figures in what is sometimes termed the "Irish national memory." There, when he is remembered at all, it is as a traitor to Ireland, responsible for the oppression of his own race and for postponing by eight centuries the emergence of a national state. It has been with some vigour that Irish historians have taken on the task of revising this view, and although a scholarly biography has yet to be published on Mac Murchada, they have been generally successful. Leaving to one side the problems with teleological history that links twentieth-century problems with twelfth-century events, Mac Murchada’s "treasonous" actions have become comprehensible, even natural, when he is studied in his own context.

Background and Early Career

We have an unusually full knowledge of Diarmait Mac Murchada because we can supplement Gaelic sources for his career, such as the annals and the Book of Leinster, with two Anglo-Norman texts documenting the invasion of Ireland: the Expugnatio Hibernica ("The Conquest of Ireland") by Giraldus Cambrensis, and the metrical history in French known as the Song of Dermot and the Earl. Nonetheless, his early career remains relatively obscure. Giraldus included a description of Diarmait in his work on the conquest of Ireland:

Diarmait was tall and well built, a brave and warlike man among his people, whose voice was hoarse as a result of constantly having been in the din of battle.

It is not hard to believe that, by the time the first Anglo-Norman adventurers met Diarmait in the late 1160s, a career spent striving to maintain his position had hoarsened his voice.

The homeland of the Meic Murchada dynasty was Ui Chennselaig, a region in south Leinster with its center at Ferns in modern County Wexford. Leinster was traditionally ruled by the Ui Dunlainge dynasties of north Leinster. Following the battle of Clontarf in 1014, political instability within the north Leinster dynasties, and their rivalry with the Meic Gilla Patraic of Osraige in south Leinster, enabled a particularly able king of Ui Chennselaig to seize the kingship of Leinster in 1042. This was Diarmait mac Mael-na-mBo (d. 1072). He went on to take the kingship of Dublin in 1052 and to lay claim, admittedly with opposition, to the kingship of Ireland. From the death of Diarmait mac Mael-na-mBo until the coming of the Anglo-Normans, the kingship of Leinster remained in the hands of the Ui Chennselaig—an extraordinary feat for a small and previously unimportant kingdom from south Leinster.

Diarmait Mac Murchada was a great-grandson of this king, and he is said to have succeeded his brother Enna as king of Leinster in 1126. He can, in truth, have been little more than king of his homeland of Ui Chennselaig at first. The intervening Leinster kings had not retained the power that mac Mael-na-mBo had attained, and Diarmait—who succeeded aged only about fifteen—was by no means secure. He was threatened by dynastic, provincial, and interprovin-cial enemies. There were certainly others among the Ui Chennselaig who could have put aside the claim of a youth like Diarmait, and the northern dynasties that had lost the Leinster kingship less than a century before were typically hostile. In terms of external enemies, the threat to Diarmait is obvious from the first reference to him in the annals. In 1126, they report that the king of Connacht, Tairrdelbach Ua Conchobair, marched into Leinster and deposed "the son of Mac Murchada"—an inauspicious start to a career. In order to succeed, then, Diarmait was going to have to fight.

Diarmait’s early career was spent consolidating his position in Ui Chennselaig and then asserting his power over Leinster. Tairrdelbach Ua Conchobhair had supported the claim to the kingship of Leinster of one of the Ui Faelain, a north-Leinster dynasty based in modern Kildare. Domestic trouble in Connacht in the 1130s, however, weakened Ua Conchobair’s influence in Leinster affairs and allowed Diarmait to come to prominence. He did this spectacularly by perpetrating a notorious outrage on the abbess of Kildare. Kildare, with its shrine to St. Brigit, was Leinster’s foremost monastic institution, and the king of Leinster traditionally held the right to appoint the abbess. In 1132, the incumbent was an Ui Faelain appointee. Diarmait wished to make way for his own candidate and had the abbess’s suitability destroyed with a ruthless expedient. As the annals put it: "The nun herself was taken prisoner and put into a man’s bed." His hold on Leinster was similarly maintained with severity. In 1141, the north-Leinster dynasties rose against Diarmait. He crushed the rebellion and had seventeen dynasts from Ui Dunlainge families and an unspecified number of lesser nobles killed or blinded. This was an atrocity even for Diarmait’s contemporaries. A similar action in 1166 precipitated the fall of the king of Ireland, Muirchertach Mac Lochlainn. The twelfth century was not an exclusively violent time. The annals, although replete with military hostings and depredations, also report a great number of peace conferences mediated by the church and reminiscent of the peace movements on the European continent a century earlier. Diarmait had established himself as a ruthless ruler. It was a point that impressed Giraldus Cambrensis, who remarks, "He [Diarmait] preferred to be feared by all rather than loved."

Interprovincial Politics and International Contacts

By 1142, with his rivals in north Leinster devastated, Diarmait was strong enough to become involved in interprovincial politics. His policy was expedient: he cooperated with whomever would best serve his interests. It is not the case that throughout his career he harbored a grudge against the kings of Connacht and sought his political and military allies in the north. Indeed, in the early 1140s he struck up an alliance with Tairrdelbach Ua Conchobair based on their mutual enmity for the Ui Briain of Munster. It is true that Tairrdelbach’s son, Ruaidn Ua Conchobair, later became a bitter enemy of Diarmait and was instrumental in his downfall in 1166. But this was in the future. Until Tairrdelbach’s death in 1156, Diarmait’s interests were best served by not crossing the Connacht king. Diarmait’s concerns were twofold: to secure control over Osraige as a buffer between himself and the Ui Briain of Munster, and to exert influence in the affairs of his northern neighbor Mide. In both these matters Tairrdelbach Ua Conchobair was to help him.

That Diarmait was not merely ruthless but also politically adept is shown by his actions in 1151. In that year, he and Tairrdelbach Ua Conchobair inflicted a crippling defeat on Tairrdelbach Ua Briain at the battle of Moin Mor. This victory gave Diarmait enough power to intervene in Osraige and appoint kings favourable to him. There was, however, a new power growing in the north of the country in the form of Muirchertach Mac Lochlainn, king of Cenel nEogain. Mac Lochlainn and Diarmait, although they were allies later, were not initially well disposed toward each other. This was particularly true after Diarmait’s joint action with Mac Lochlainn’s principle rival— Tairrdelbach Ua Conchobhair—in destroying Ua Briain at Moin Mor. The same year, following his victory in Munster, Diarmait sent Mac Lochlainn the hostages of Leinster, seemingly of his own free will. In was a shrewd political move designed to avoid the enmity of Mac Lochlainn without preventing Diarmait from acting with Ua Conchobair when it suited him. In this way, Diarmait maximized the chances of securing his interests.

In 1152, with his control over Osraige newly secured, Diarmait involved himself in the affairs of Mide. In concert with Ua Conchobair and Mac Lochlainn, he attacked Tigernan Ua Ruairc (d. 1172), the king of Breifne, and notoriously kidnapped Ua Ruairc’s wife, Derbforgaill. Both Gaelic and Anglo-Norman sources report this tale with relish, but they vary on the question of motive. The Annals of Clonmacnoise report that Diarmait wished "to satisfie his insatiable, carnall and adulterous lust." The Song of Dermot and the Earl, however, portrays the unfortunate Derbforgaill as a pawn in Diarmait’s power game with Ua Ruairc:

Dermot, king of Leinster, Whom this lady loved so much, Made pretence to her of loving, While he did not love her at all, But only wished to the utmost of his power [to be avenged on Ua Ruairc].

It was supposedly in retaliation for this that Ua Ruairc insisted on Diarmait’s expulsion from Ireland, which led directly to the appeal to King Henry II. In fact, Diarmait’s flight from Ireland came some thirteen years after the kidnapping. Moreover, in 1166, Ua Ruairc was an ally of Ruaidrf Ua Conchobair, whose father Tairrdelbach had been allied with Diarmait in the attack on Ua Ruairc in 1152. Neither of these facts has, however, prevented the two events’ being directly connected in popular imagination. The historian F.J. Byrne snubbed both this interpretation and Derbforgaill with the memorable comment that "[she] may have been fair, but was certainly forty." Instead, he attributed Ua Ruairc’s hostility to his long-standing rivalry with Diarmait over Mide. Nonetheless, there can be little doubt that the Derbforgaill affair added a personal edge to an already acrimonious relationship.

The death of Tairrdelbach Ua Briain in 1156 altered the political situation in Ireland. Muirchertach Mac Lochlainn was now without serious rival, and Diarmait threw his lot in with him; Tigernan Ua Ruairc was soon associated with the new king of Connacht, Ruaidrf Ua Conchobair. It was at this time that Diarmait began to take a serious interest in the Ostman cities of Leinster. His great-grandfather, Diarmait mac Mael-na-mBo, had set a precedent of taking the kingship of Dublin in 1052, but it was some time since more than a nominal submission had been wrung from what was emerging as the capital of Ireland. In 1162, aided by Mac Lochlainn, Diarmait forced Dublin to submit and according to the annals "obtained a great sway over them, such as was not obtained for a long time." It was his connection with the foreigners or "Gall" of Dublin, and not his appeal for Anglo-Norman aid, that won for Diarmait the nickname "Diarmait na nGall."

Diarmait already had a long association with Dublin. He had founded the Augustinian nunnery of St. Mary de Hogges there in 1146, and sometime after 1161 established the priory of All Hallows on the site now occupied by Trinity College, Dublin. This relationship is instructive in terms of assessing his subsequent appeal to King Henry II. Through trade and its coveted fleet, Dublin had a centuries-old relationship with Wales and England. Previous kings of Leinster, in claiming authority over the city, were thereby brought into this transmarine network [see Anglo-Irish relations]. But one does not have to dig so far into the past for an association. In 1165, the native Welsh chronicle reports that Henry II hired a fleet from Dublin to fight in his abortive Welsh campaign of that year. Diarmait, in control of Dublin, surely had knowledge of this, possibly indicating a connection with Henry II dating from only one year prior to Diarmait’s flight from Ireland in 1166.

Diarmait’s power was now bound up with Mac Lochlainn, and when the latter fell in 1166 Diarmait’s enemies, Ua Conchobair and Ua Ruairc, rapidly moved against him. The men of north Leinster and the Ostmen of Dublin took the opportunity to rebel, and Diarmait was forced to retreat to his heartland of Uf Chennselaig. He then took the decision to sail to Bristol and seek out Henry II [see Anglo-Norman Invasion]. He was back in Ireland with a small group of Anglo-Norman adventurers by 1167, and Ruaidrf Ua Conchobair, now king of Ireland, allowed him to retain his homeland of Uf Chennselaig. Diarmait was, however, set on greater things and had promised his daughter in marriage and the succession to Leinster to the earl of Pembroke, Richard de Clare (Strongbow), who arrived in Ireland in 1170. By the time Diarmait died at his capital of Ferns around May 1171, his Anglo-Norman forces—although not yet entirely secure—had destabilized the political situation in Ireland, causing other Irish kings to go into rebellion and shattering the power of Ruaidrf Ua Conchobair. They were successful enough to bring Henry II to Ireland late in 1171. With that royal expedition, the history of the English lordship of Ireland began.


Historians debate the importance of Diarmait Mac Murchada. Arguing counterfactually, they question whether, even had he never appealed to Henry II, the situation would have been very different. Sooner or later, it has been said, an English king would have turned to a conquest of Ireland. Diarmait was merely a facilitator. Perhaps, but conquest did not necessarily have to take the form it did in Ireland. The "Normanizing" kings of Scotland, notably David I (1124-1153), show that Anglo-Norman culture could become influential by subtle infiltration as well as by invasion. It is therefore still open to question whether Diarmait’s submission to Henry II made a full conquest of Ireland inevitable.

Another theme that has been stressed is that Diarmait’s actions were not so extraordinary. In twelfth-century Ireland, kings were willing to adopt new methods to achieve and sustain their power. We should remember that requests for foreign aid were not exceptional and were naturally directed to the military source closest to hand. Ulster, for instance, had intimate contacts with the western isles of Scotland. As recently as 1154, Muirchertach Mac Lochlainn had hired a fleet from the isles led by one Mac Scelling to counter the naval power of Tairrdelbach Ua Conchobair. Mac Murchada’s contacts in Leinster lay east and south; so it was that in 1166 he set sail for Bristol.

These views have won general acceptance; the only danger is that, as revisions turn into threadbare commonplaces, the significance of Diarmait will be explained away. He was—even by the standards of his time—a ruthless and manipulative ruler, and he would have had a reputation as such without any invasion. Recourse to foreign aid may have been natural step for him. But that should not dilute the fact that the Anglo-Norman invasion was the single greatest watershed in Irish history after the conversion of Ireland to Christianity, and Diarmait Mac Murchada was central to it.

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