The Anglo-Norman Invasion of Ireland: The Tale of the Betrayer King
History is full of watershed moments—points in time so pivotal, so foundational, that the consequences of their events ripple across the annals and can still be felt decades, centuries, even millennia later. The assassination of Archduke Franz Ferdinand at the hands of Gavrilo Princip in Sarajevo, 1914; Julius Caesar’s crossing of the Rubicon in 49 BCE; the death of King Philip II in 339 BCE, and the ascendancy of his son, Alexander, to the throne of Macedon. Such moments might bring to mind the Great Man Theory of History, an observation made by the Scottish philosopher Thomas Carlyle in 1841, in which he confidently stated that “the history of the world is but the biography of great men.” While most modern historians rightly argue against the theory’s disenfranchising undercurrents, it’s difficult to deny the presence of the powerful personalities that so often live at the center of these tumultuous times. It must be said, however, that not all watershed moments break for the better—and not all of these “Great Men of History” are, in reality, all that great.
This will be the first in a series of essays about one such historical watershed moment: the Anglo-Norman invasion of Ireland in the twelfth century. This event would alter the very fabric of the island and set its people on a course for eight hundred years of colonial exploitation and destruction—first at the hands of the Normans, then the English, and finally, the British. Through the unique lenses of the individuals who played key roles in these events, I intend to examine motivations, impulses, and the long-term effects of the cascading decisions made nearly one thousand years ago—the echoes of which can still be heard and felt today. Our first steps into this ancient world of barons, kings, and high kings will be taken in the shoes of, as of 1166, the erstwhile King of Leinster, Diarmait mac Murchada: a man known to history not just for his viciousness, petulance, and ambition, but for his deep involvement in the events that changed the fate of Ireland forever. Before we begin in earnest, however, let us first set the political scene in the Atlantic Isles in the middle of the twelfth century.
In the years leading up to Strongbow’s landing at Waterford in 1170, the island of Ireland was a divided and fragmented place. Each of the island’s five provinces—Ulster, Munster, Connacht, Leinster, and Meath—was ruled by lords and barons; all paid homage, however, to the province’s Rí, or king. Furthermore, allegiances within and beyond these over-kingdoms were in a constant state of flux, as Rí battled Rí for the honour and title of Ard Rí—High King. Though the largely symbolic high kingship depended on complex webs of favour, military leverage, and fickle loyalties, it remained a much-sought-after position. The division it wrought across the island would only serve to ripen it for the eventual picking.
Some one hundred years earlier, across the Irish Sea, the Anglo-Saxons of Britain had experienced their own invasion. In 1066, William of Normandy arrived on their shores and laid claim to the island’s wealth and produce. Over the ensuing century, the Normans would make the island their home—and although they remained keenly aware of the verdant lands to their west, connection and communication between the two islands remained loose at best. Of course, merchants from Bristol might have braved the narrow channel to flog their wares in one of the Viking settlements on Ireland’s east coast; or perhaps Irish mercenaries found employment under the newly minted Norman lords of the English Marches. These associations, however, would have been the exception rather than the rule. This is not to say that the marauding, conquering Normans had no designs on the land next door. King Henry II had even been granted permission to annex the island via a papal bull from Pope Adrian IV, with the intention of bringing Ireland’s semi-autonomous church back into the fold of Rome. He was busy, however, consolidating his kingdom across Britain and France—and so Ireland, for the moment, was left largely alone.
That was until the fateful events of 1166, in which the High King, Ruadrí ua Conchobair, ousted the King of Leinster in a violent deposition. Desperate for recourse, Diarmait mac Murchada turned eastward—and in doing so, drew the watchful eyes of ambitious lords and insecure kings toward lush Hibernia. But who exactly was Diarmait mac Murchada, and what drove him to invite the wolves at Ireland’s door inside and out of the cold? Was he a man of pure, unadulterated ambition—or simply a product of the fragmented society and times that forged him? To find out, let us examine his early life and the events that led up to his overthrow at the hands of the High King.
Mac Murchada as he appears in the Expugnatio Hibernicam, by Gerald of Wales
Born circa 1110, Diarmait was the second eldest son of the then King of Leinster, Donnchadh mac Murchada. As a young lad, he would have received a noble’s upbringing—this meant an education in leadership, military strategy, and the dynastic politics of his homeland. The written records from the years leading up to his ascension are sparse, but what little survives speaks of a Leinster kingship in constant flux, changing hands regularly around the time of his birth. His father died when Dairmait was still a boy, and the crown passed around many heads before finally settling atop that of Domnall ua Faeláin, a minor king already ruling a small kingdom in south Leinster known as the Déisí. This was likely at the behest of then High King Toirdelbach ua Conchobair (father of Ruaidrí), who had a vested interest in keeping the power of the Mac Murchada’s at a low boil. Diarmait, however, would make his feelings about a usurper sitting on his father’s throne abundantly clear. In 1132, he made a startling debut on the Irish political stage: he captured Ua Faeláin, put out his eyes, and seized the kingdom of Leinster for himself.
By blinding his rival, Mac Murchada ensured that Ua Faeláin would never again be fit to rule or challenge him. Though a relatively common practice in medieval Ireland, the act was still regarded as a particularly brutal means of destroying a political enemy—and the nascent king must have been keenly aware of the signals he was sending. As such, the blinding of Ua Faeláin serves not only as an insightful glimpse into Mac Murchada’s true character—he would reach for this particular tool once more before too long—but also as a powerful warning of his ambitions to his contemporaries across the island. After all, it was the High King who had ordained Ua Faeláin as King of Leinster, and Mac Murchada’s actions were a direct affront to his authority.
In the decades that followed, Diarmait mac Murchada’s kingship was marked by naked aggression, shifting alliances, and a perilously poised relationship with his overlord. The King of Leinster spent the next ten years violently consolidating his power over the lords of his province, while High King Ua Conchobair took his homage at face value, and allowed him to operate unimpeded. It would not be long, however, before Mac Murchada once again demonstrated to the entire island the true extent of his ruthlessness.
The taking of hostages as security was a common political tool used widely across medieval Europe. Hostages were leveraged to ensure the loyalty of subordinate lords and to enforce their good behaviour should they begin to form designs on a higher station. Though Ireland’s political landscape was far more fragmented than that of the continent, it was no exception to this common paradigm. High King Ua Conchobair ruled from his seat in the west, in Connaught, and relied heavily on the practice to shore up his power base across the provinces. Historians believe that Mac Murchada was tasked by Ua Conchobair with caring for a cohort of these hostages—likely a group of noble youths, the sons of Connaught's lords. While Mac Murchada deigned to facilitate his overlords command, he also used the opportunity to send his clearest message yet. Reaching for the same brutal tactic he had once used against Ua Faeláin nearly a decade previous, in 1145, he blinded the young men in his care, sending shockwaves of scandal and disgust around the country. The High King would make no immediate retaliation, but this moment surely marked the lifting of the veil of deference—and the true souring of their relationship.
Nor was Ua Conchobair the only recipient of this terrible message. The blinding of the Connaught hostages cemented Mac Murchada’s reputation as dangerous and unpredictable—not least in the eyes of the lords of the west, whose children were among those maimed, and who swore fealty to the High King himself. This lens offers a particularly interesting perspective from which to examine Mac Murchada’s next recorded malfeasance. Perhaps he was compelled to live up to the notoriety he had fostered. Perhaps, as later accounts would suggest, the King of Leinster did what he did out of love. Or perhaps—and in this writer’s opinion, most likely—the abduction of a rival’s wife (along with her cattle and furniture, mind you) was a barefaced, high-stakes political gambit. According to the Annals of the Four Masters, in 1152 Diarmait mac Murchada abducted Derbforgaill, the wife of Tigernan ua Ruairc, lord of Bréifne. Most historians agree that the kidnapping was likely orchestrated by Derbforgaill’s brother—then King of Meath—in an attempt to weaken Ua Ruairc’s standing and strengthen the Leinster-Meath alliance. Though this slight, too, would go largely unanswered, the resentment it planted in Tigernan ua Ruiarc would fester like carrion in the hot sun—and provide yet another name for Mac Murchada’s ever-swelling list of enemies.
Ferns, the religious and political capital of Mac Murchada’s Leinster. Here is the abbey as it lies today.
Readers would be forgiven if the image of Mac Murchada currently forming in their mind was less than pleasant, but none of this is to say that he was an entirely despicable man. Credit where credit is due: it would appear that the King of Leinster cared greatly for the condition of his immortal soul. Between the political treachery, the maimings, and the needless violence, Mac Murchada still found time to advocate strongly for the Irish Church—particularly in support of its efforts toward Gregorian reform. In 1158, he founded Ferns Abbey and ordered it administered under the governance of Rome; later, he would make it both the religious and political centre of his kingdom. Though widely lauded in ecclesiastical records for his contributions to Catholic security in Ireland, this writer finds it difficult to reconcile his abundantly violent character with the generosity and charity he extended towards the Church. Perhaps it’s cynical to consider that Kings who encouraged continental monasticism amongst their subjects were supported and favoured by the Roman Catholic Church; perhaps even more so to suggest that Mac Murchada likely leveraged his favour with the Church to offset his reputation for duplicity and callousness.
By the middle of the century, the elegy of Diarmait Mac Murchada was approaching a crescendo—one that would see the reaping of all he had sown and permanently change the face of Ireland. The stirring of this sombre piece began with the death of Toirdelbach ua Conchobair in 1156 and the ascension of his son, Ruaidrí, to the high kingship. Ruaidrí would prove a far more proactive regent than his father, and in 1166, he demonstrated to Mac Murchada the dangers of cultivating so many powerful enemies.
At the beginning of that fateful year, the newly incumbent High King was intent on cementing his power and stamping out any who might oppose his authority. To that end, he raised the support of kings and lords across the northern half of the island with the express intent of laying low the belligerent and detested Diarmait mac Murchada. Perhaps, too, he sought to right the wrongs committed against his father, and in that moment, saw the perfect opportunity to do so. Although we may confidently speculate on the true motives of Ruaidrí ua Conchobair, there can be little doubt about those of the man who would play a central role in the campaign to come: Tigernán ua Ruairc. Though Derbforgaill had been returned safely to her husband a year after her abduction, Ua Ruairc still nursed an all-encompassing grudge—and had no doubt had been waiting with bated breath for the moment he might take his revenge. That moment would arrive—for him, and for many of the Leinster lords fed up with Mac Murchada's rule—in 1166, when the High King came calling.
The coalition they formed swept through the east of Ireland like a hot knife through butter, making quick work of a politically isolated and unsupported Mac Murchada. Crucially, however, the soon-to-be-former King of Leinster escaped death and detainment by spiriting himself away before the fall of his capital, Ferns. Now in exile, Mac Murchada found himself a deposed king—and resolved, at whatever cost, to reclaim his throne. To do so, he would have to leave Ireland and cross the narrow channel to Britain.
A particularly deferential Mac Murchada, and his new King, Henry II
Landing first in Bristol and then making his way to Aquitaine, France, Mac Murchada leveraged his reputation to secure an audience with King Henry II, from whom he sought help in taking his own turn at revenge. Ever the shrewd operator, Henry offered the ex-king no direct assistance, but instead granted him permission to recruit mercenaries from among his vassals—namely, the Norman lords of Wales and the English Marches. This approach served Henry twofold: firstly, it enabled him to freely extend Anglo-Norman influence into Ireland at little cost to himself; secondly, it opened the doors for his intervention at a later date. In exchange for his generosity, Norman records hold that Mac Murchada swore fealty to the English king, and promised to hold Leinster as his client-kingdom should he be successful in reclaiming it. Though the Irish sources are conspicuously silent on this point—telling, in and of itself—if true it marks the moment in which the Anglo-Normans first found purchase on the cliff-face of the conquest of Ireland; a watershed moment, indeed.
By 1167, Mac Murchada had returned to Bristol, where he actively began a recruitment campaign. Though initially met with lacklustre support and interest, he would soon secure an all-important and historic alliance with the Earl of Pembroke—a man who would soon become known as Strongbow: Richard fitz Gilbert de Clare. Desperate to win the support of the ambitious baron, Mac Murchada not only offered him his daughter’s hand in marriage but also promised him the succession to the Kingdom of Leinster. For those keeping track, this offer marks the second time Mac Murchada has compromised the sovereignty of his homeland in favour of a foreign power—and in my mind justifies the provocative title of this essay. In the eyes of De Clare, however, it was an offer too rare and lucrative to pass up. With his standing at court at an all-time low due to the mismanagement of his earldom, surely De Clare saw Mac Murchada’s offer as an opportunity to win back the King’s favour? Failing that, perhaps he viewed it as a chance to start fresh, and build a life unfettered by an absentee king.
It was in May of 1169 that Diarmait Mac Murchada finally found his way back to Ireland; he landed in Bannow Bay, County Wexford, with a thousand men at his back. De Clare and his contingent would not arrive until August of the following year, but Mac Murchada made good use of the time and resources available to him in the interim—making short work of the Wexford defences, he captured the town within two days of landing. One can easily imagine High King Ruaidrí ua Conchobair roused from a disturbed sleep at the very moment Mac Murchada’s boot touched Irish soil, drenched not just in cold sweat but in the premonitory anticipation of an impending disaster. Before the year was out, both parties signed what would come to be known as the Treaty of Ferns: a set of accords that reinstated Mac Murchada as King of Leinster, albeit under certain conditions. First, Mac Murchada was to expel his Anglo-Norman allies and send them back to Britain. Second, he was to formally recognise Ua Conchobair as his overlord. And third, he was to give up his son as the High King’s hostage—an assurance that he would behave himself moving forward. The fact that Ua Conchobair, who held both the military advantage and the support of the Irish lords, signed such a treaty has raised historian’s eyebrows for generations. Perhaps he had the foresight to see what the arrival of the Anglo-Normans would truly herald, and sought to conserve his strength for the battles to come. Or perhaps the toll taken by the civil strife of 1166 still clung to the island’s consciousness, and Ua Conchobair, in that moment, saw the former king as nothing more than a dog with a bone. He might be forgiven if he believed it simpler to just let him have it.
But the Treaty of Ferns would not hold for long. Mac Murchada, now once again King of Leinster, neglected to send his Anglo-Norman friends away—quite the contrary, in fact. Richard “Strongbow” de Clare had spent the preceding year coiled like a viper, waiting for the perfect moment to strike. Now, with the success of Mac Murchada’s enterprise shining just beyond the horizon, he did exactly that. He landed on the shores of Wexford with another Norman force in the Summer of 1170. Things moved quickly then: Strongbow married Mac Murchada’s daughter, Eva of Leinster; Mac Murchada marched on Wexford with the combined Anglo-Norman forces and swiftly subdued the besieged city; then, their appetites whet and their blades sharp, they turned their sights on Dublin. In response, High King Ua Conchobair executed Mac Murchada’s son—revealing the relentless character of both men—and set about reforming the coalition that ousted the King of Leinster three years prior. As the Anglo-Norman army approached the affluent port town, so too did the native force march to defend it.
The Marriage of Strongbow and Eva of Leinster, set against the ruins of Wexford
A strategically important trading port, Dublin was ideally positioned on the lip of the Irish Sea and had been ruled by the Norse-Gaelic since the beginning of the twelfth century. In the autumn of 1170, the throne was occupied by Ascall mac Ragnaill, a king loyal to Ua Conchobair and one who surely believed in the inevitable victory of the Leath Cuinn (Conn’s Half, or the Northern Half of the Island) coalition. But in a stunning manoeuvre, Mac Murchada and his host made their way through the Wicklow uplands and launched a surprise attack on their enemy’s flank, who, believing it the most likely path of the approaching force, were dug in near modern-day Clondalkin. The Anglo-Norman forces caught the Gaels completely by surprise, storming Dublin and taking it with little resistance. Ascall mac Ragnaill fled, leaving his people to the wolves, and faded appropriately from history.
Once a brutal king, then a betrayer king, and finally a beggar king—but now Mac Murchada found himself in a position of power unprecedented in eastern Ireland: he was the King of both Leinster and Dublin. De Clare’s position, too, was consolidated—not only had he married Eva of Leinster, but he had also effectively become the heir to that very same throne.
The High King would be loath to take this thrashing lying down. Taking the remnants of his Grand Armée, he laid Dublin under siege in 1171. Though the assault lasted months, it failed to break the city’s defences, and it wouldn’t be long before De Clare and his Anglo-Norman forces launched a daring counter attack. This sally would route Ua Conchobair's forces, lifting the siege and forcing the High King’s withdrawal—an embarrassment that irreparably damaged his standing amongst the Irish kings and lords. For Mac Murchada, the result of the siege of Dublin was the further cementing of his power, and his installation at the head of the most powerful, most feared bloc in all of Ireland; For Ua Conchobair, it was the end of his reign as High King.
It’s here that we must bring our tempestuous—and frequently frustrating—tale of unchecked ambition, avarice, and greed to an end. In May of 1171, on what was likely a warm, balmy day on the east coast of Ireland, Diarmait mac Murchada died of natural causes in his capital of Ferns—no doubt wistfully, dreaming of what might have been had he been granted just a few more years. The utter quagmire left in his wake, however, would remain. His death threw Leinster and Dublin into a crisis of succession: Irish nobles rejected De Clare’s claim, arguing that a foreigner couldn’t possibly inherit an Irish kingship. This objection set Strongbow and the Irish nobility on a collision course—the story of which must be saved for another in this series of essays. This tale, it can safely be said, will feature an encore of such magnitude and importance that it would fundamentally alter the landscape of Irish political power—more so than any renegade Norman army ever could.
But King Henry II can wait. This wasn’t his story—nor is it a story that belongs to any of the Anglo-Norman kings or lords who would busy themselves laying claim to Irish lands for the next eight hundred years. This has been the story of Diarmait mac Murchada: a barbarous and conniving man whose lust for power and greed set his homeland on a course of subjugation and colonisation, and over the centuries, one that would cost it its ancient and vibrant culture. Here was a man who felt no obligation to decency, who prized might and imperiousness above all else—so much so that he willingly sacrificed the life of his own son to further his goals. While it’s likely that the marauding, conquering Anglo-Norman’s would have turned their sights westward sooner or later, as an Irishman, this writer can’t help but lay much of the responsibility for our cultural and linguistic destruction at this man’s feet. The tempering of Britain's imperial steel—and the tactics they would learn to subjugate the peoples of India and South Africa—took place in Ireland, and the generational trauma it caused can be traced back to the moment Mac Murchada decided to set sail for an audience with King Henry II.
Nowadays, if one were to take a stroll through any of this island’s beautiful towns (save, perhaps, for Ferns) and ask a local what they thought of the former King of Eastern Ireland, Diarmait Mac Murchada, one would likely be met with confused or dubious expressions. His name is not one well known in the Ireland of 2025—and I can’t help but wonder whether or not that’s for the best.