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Segment of 18th-century illustration of Brian Boru. Source: Public domain

The Legendary Brian Boru: Ireland’s Greatest King


Brian Boru was Ireland’s greatest conqueror and the first man to unite the Emerald Isle into one realm, rising above the divisions of the squabbling Irish elite and their 150 kings. As well as competing with a large array of domestic enemies, Brian also had to deal with the Norsemen of Scandinavia, a band of violent pirates from abroad who over the years had begun to settle much of the eastern and southern parts of Ireland. Inspired by the valiant deeds of his grandfather, father, and brothers, Brian Boru would go on to complete their work after his ascendancy to the throne in 976, leaving a legacy that has since become legendary.

Brian Boru and the Dál Cais Clan

Brian Boru was born in 941 into the Irish clan known as Dál Cais who ruled over Tuadmumu, in northern Munster. At the time, despite having a population of only 500,000, Ireland was divided into 150 different kingdoms, and so Brian’s birth was not deemed as being particularly special. As well as having to contend with other fiefdoms, each Irish kingdom was plagued by division, disunity, and factional strife.

The Dál Cais was no different, and throughout Brian’s early life his lineage, known as the Uí Thairdelbaig, competed with the Eóganachta, a rival bloodline, for control over northern Munster. In a sign of how inter-related the aristocracy of Munster was at the time, both dynasties were actually descendants of the same man, Eógan Már, who formerly exercised dominance over Munster and the neighboring region of Cashel several generations earlier.

Nevertheless, by the 8th century, Brian’s ancestors had managed to establish a foothold in East Clare, from where they were able to expand over the following decades. In 934, only a few years before Brian’s birth, and under the leadership of Brian’s legendary grandfather Lorcán, the Uí Thairdelbaig managed to impose their authority over the whole of Munster, pushing out the Eóganachta. In a nod to their shared ancestry, the Uí Thairdelbaig renamed themselves the Dál Cais having finally achieved the dominant position within the ancient family tribe.

But Lorcán may not have done this alone, and many have speculated he was helped by the Uí Néill, an influential Irish family who were traditionally the Irish High Kings, the most powerful warlords in all of Ireland. The man who held this esteemed post during Lorcán’s day, Donnchad Donn mac Flainn, married Órlaith, Brian’s sister and the daughter of Cennétig, who was Brian’s father, in a marriage which suggested that an alliance had taken place between the two noble houses.

The Uí Néill, however, remained the preeminent partner, and could exercise their power at will against the weaker Dál Cais when they thought it was appropriate. In 941, Órlaith was executed by her husband, Donnchad, for committing adultery against him with his own son. The Dál Cais could do nothing against the Irish High King, and it’s likely that they were unable to intervene when she was put to death. In a premonition of what was to come, however, Brian Boru was born that same year, and thanks to his courageous efforts the balance of power would shift dramatically in his family’s favor to heights previously unseen.

The print entitled “The noble sons of Ireland” depicts prominent men from Irish history, including Brian Boru in the ninth position from the left. (Public domain)

The print entitled “The noble sons of Ireland” depicts prominent men from Irish history, including Brian Boru in the ninth position from the left. (Public domain)

The Rise to Prominence of Brian Boru and the Dál Cais Clan

Before the Dál Cais could begin to dominate the Uí Néill, they first had to deal with a familiar enemy closer to home. Following the accession of Cennétig to the Munster crown in 944, the Dál Cais suffered a heavy defeat at the hands of their rival bloodline Eóganachta, whose fortunes had revived. Two of Brian’s brothers, Fin and Dub, were killed during the battle, the first of many tragedies in Brian Boru’s life.

Despite this crushing loss, the Dál Cais were able to maintain their dominance and by 950 they were considered such a threat by the new Irish High King, Congalach mac Máele Mithig, that he undertook a campaign into the heart of Munster in order to prevent further expansion. In the subsequent skirmish, two more of Brian’s brothers, Echthigern and Donncuan, also died in defense of their homeland.

In 951, when Brian Boru was just 10 years old, his father King Cennétig passed away. The high titles bestowed upon the deceased sovereign illustrated that that he had ended a life of great honor, repelling two great adversaries, the Eóganachta and Uí Néill, from his ancestral property in the process.

What followed was a period of instability stirred up by weak leadership, with Brian’s brother Lachtna killed within two years of his reign. However, by 959 the situation had steadied as another of Brian’s brothers, Mathgamain, became chieftain. Mathgamain was an accomplished general, conquering the province of Cashel, usurping from the Eóganachta the title of “King of Cashel.”

In 967, spurred on by his early momentum, Mathgamain turned his attention to the Norsemen of Limerick, defeating them soundly at the Battle of Sulchóit. It was here that Brian Boru, now in his mid-twenties, first burst onto the scene, distinguishing himself on the battlefield with great heroism and bravery. His actions that day are described in the Cogad Gaedel re Gallaib, a chronicle of Brian’s life written by his great-grandson:

“There were then governing and ruling this tribe two stout, able, valiant pillars, two fierce, lacerating, magnificent heroes, two gates of battle, two poles of combat, two spreading trees of shelter, two spears of victory and readiness, of hospitality and munificence, of heart and strength, of friendship and liveliness, the most eminent of the west of Europe, Mathgamain and Brian, the two sons of Cennétig.” (Cogad Gaedel re Gallaib as cited by Duffy)

For the next nine years, Brian Boru would serve as Mathgamain’s loyal lieutenant, as the brothers overcame the usual sibling rivalries afflicting most Irish gentry, becoming best friends and loyal allies.

Brian Boru sculpture outside Chapel Royal outside Dublin Castle. (Marshall Henrie / CC BY-SA 3.0)

Brian Boru sculpture outside Chapel Royal outside Dublin Castle. (Marshall Henrie / CC BY-SA 3.0)

Brian Boru Becomes King

In 976, however, disaster struck. Mathgamain was captured and killed by the Norsemen of Limerick taking revenge for the Battle of Sulchóit. In that same year Brian Boru replaced Mathgamain as king, vowing to avenge his brother’s cruel death. In 977 Brian’s men mercilessly hunted down the leader of the Limerick, King Ívarr, committing sacrilege by striking them down within the precincts of the sacred site of St. Senan on Scattery Island.

Brian’s wins over the Norse were supplemented by the extermination of the Eóganachta, a recurring thorn for the Dál Cais. In the years following Mathgamain’s death, the Eóganachta had managed to reclaim the title of King of Cashel proclaimed by the late king. In 978, at the Battle of Belach Letaha, Brian took back his brother’s title in a decisive engagement against their family nemesis and by the end of the 970s, Brian had mastery over Munster. For Brian, it was now time to pursue even grander ambitions and to achieve even greater accomplishments.

His path to glory started in 982, when his armies attacked the neighboring Osraige, which had acted as a buffer state against the Duchy of Leinster, the traditional demesnes of the Uí Néill and the Irish High Kings. The move had shown all of Ireland that Brian harbored royal pretensions. In reaction, the Uí Néill destroyed the tree of Mag Adhair, the site where the Dál Cais customarily inaugurated their kings, as a demonstration of their disproval of Brian’s lofty aims.

Unperturbed, Brian continued his assault, confirming the submission of Osraige by the taking of hostages and devastating the lands of Leinster in 983. For the rest of the 980s, Brian found himself in a strong position and effectively dealt with any problems that came his way. In 985 for instance, the Déisi, a subjugated people in the southeast of Munster, were harried and overwhelmed by Brain’s forces after stealing 300 cows.

In 986, during an episode of court intrigue, he imprisoned his nephew Áed, son of Mathgamain, who challenged his overlordship. In a sign of respect for his fallen brother, Áed was kept alive and eventually re-integrated back into the family fold, where he died with honorable titles in 1011, illustrating Brian’s capacity to show mercy.

Finishing off the decade, Brian exacted retribution for the demolition of the tree of Mag Adair, harrying Uí Néill’s lands once again and trespassing on their own coronation place at Uisnech, in the most blatant expression yet of his aspiration to take the throne of the High King of Ireland for himself.

The Remarkable Unification of Ireland

Brian Boru’s plans however, did not get off to the most auspicious of starts at the beginning of the 990s. Between 990 and 993 Brian was routed several times by the Irish High King, Máel Sechnaill. In 993, Brian’s soldiers were massacred by the High King, who ravaged Munster in ruthless fashion, including the immolation of an important settlement, Nenagh. Realizing that his kingdom was weakly fortified, Brian embarked on an extensive building program in 995, constructing strongholds at his bases at Cashel, Limerick, the island of Lough Gur, and other important strategic locations.

With his kingdom now more protected and better able to defend itself from outside incursions, Brain went back on the offensive, exacting revenge on Máel Sechnaill in 996 by killing 300 of the High King’s warriors and annexing parts of Leinster. Brian now controlled all of southern Ireland and had finally tipped the scales so that now the Dál Cais, at the expense of the Uí Néill, were the strongest dynasty in Ireland.

In 997, the Uí Néill of Leinster recognized the new state of affairs in a ceremony at Port Dá Chaineóc, called the Partition of Ireland, where they were stripped of their claim to control the whole of Ireland and compelled to acknowledge that they were only masters of their patrimonial base at Leth Cuinn.

Angry at the submission of the Uí Néill, in 999 the men of Leinster decided to team up with the Hiberno-Norsemen of Dublin, who also has their own grievances against Brian for his punitive measures against their people at Limerick in the 970s. In one of the most glorious moments of his career, the twin forces were convincingly trounced by Brian at the Battle of Glenn Máma. Brian pillaged Dublin for a week, enriching himself and his lords with slaves and coffers brimming with gold and silver.

In the year 1000, Brian, who was now even more dominant after his success at Dublin, betrayed his erstwhile ally Máel Sechnaill, in the first attempt ever to control the entirety of Ireland. Máel Sechnaill and his holdings at Leth Cuinn were aggressively targeted by the combined armies of Munster, Osraige, Leinster, and Dublin which Brian had at his disposal.

By 1002, at Athlone, Brian was at the apogee of his career, having attained the total submission of the Uí Néill, who now no longer held any land of their own. Brian now owned all of Ireland, the first monarch ever to achieve this feat. However, if forging a kingdom as large as Ireland was hard, holding onto it was an even more difficult task, as Brian was to experience in the following events.

The Battle of Clontarf by Hugh Frazer, 1826. (Public domain)

The Battle of Clontarf by Hugh Frazer, 1826. (Public domain)

Defending the Realm and the Battle of Clontarf

Despite the Uí Néill submission, a troublesome branch of their family tree remained holdouts for the next two years, refusing to submit. The Cenél Conaill and Cenél nEógain families eventually capitulated in 1005. It was a reality check for Brian Boru, who now faced the Herculean job of somehow holding his new lands together.

He first had to get the backing of the powerful Christian Church, which he facilitated through a donation to ecclesiastical center of Armagh. The monk who confirmed the transaction would refer to Brian as “Emperor of the Irish,” the first known occurrence of an imperial title in Ireland. It was perhaps influenced by developments on the European continent, where Emperor Otto III had named himself “Emperor of the Romans” only 10 years before.

Yet the last years of his reign were not as spectacular as his title suggested, as Brian continuously fought recalcitrant lords all over Ireland while slipping closer and closer into old age. The recently conquered north of Ireland was an area where peace was particularly hard to institute. Once again, the Cenél nEógain and their king, Flaithbertach Ua Néill revolted in 1006, and it would take Brian four more years to subjugate them.

As soon as he quelled the Cenél nEógain, their rivals, the Cenél Conaill, mutinied almost immediately against the aging monarch. Now 70 years old, Brian was evidently too tired to continue, assigning command to his sons Murchad and Domnall. By 1012, both of his northern detractors had been restrained, but before Brian could relax he was met with yet another challenge, one that would define his life’s mission.

With the men of Leinster and Osraige, Flaithbertach Ua Néill led a devastating sortie right into the heartlands of Brian’s territories, taking Kells in 1013. Eager to stamp his authority once again, the conflict came to a head at the Battle of Clontarf. The pitched battle was fought on April 13, 1014, during the Easter festival.

Brian was outnumbered as Dublin and Leinster were reinforced by Norsemen who came from the Orkney Islands at the tip of Scotland and the Isle of Mann in the middle of the Irish Sea. Unrest around the kingdom left Brain’s forces reduced considerably, with the kings of Ulster and Connaugh refusing to send troops to his aid, and the King of Meath leaving before the end of a battle because of an argument.

On that fateful Easter Friday the armies clashed on high ground near the River Tolka, which straddled the northern shore of Dublin Bay. Brian was characteristically unshakeable, heroically leading his men to an astounding victory against all the odds.

While his enemies fled however, Brian’s life would unexpectedly be taken from him. According to legend, he was struck down in his tent by a fleeing Norseman called Bróðir. The loss of Brian was compounded by the death of his son, Murchad, who became another martyr for the Dál Cais cause. After the dust had settled, both Brian and his son were laid to rest at the Church of Armagh.

The death of King Brian Boru on Good Friday 1014. (Public domain)

The death of King Brian Boru on Good Friday 1014. (Public domain)

Ireland’s Greatest King

Although Ireland mourned, Brian Boru died having achieved everything he first set out to do. In his final act at Clontarf he had not only vanquished the Ua Néill but also the Norse, who from that point forward gave up their pretensions for power in Ireland to become traders. Brian’s ultimate triumph also created the conditions which allowed the Dál Cais to dominate Ireland for the next 150 years, his bloodline surviving until the end of King Muirchertach’s reign in 1119. The echoes of Brian’s astonishing efforts would reverberate down the ages as his descendants changed the family name, proudly sporting Ua Briain instead of Dál Cais for the remainder of their time at the helm of Ireland.

Top image: Segment of 18th-century illustration of Brian Boru. Source: Public domain

By Jake Leigh-Howarth


Duffy, S. 2004. “Brian Bóruma [Brian Boru]” in Oxford Dictionary of National Biography.

Hegarty, N. 2020. Irish History: People, Places, and Events that Built Ireland. Collins.

Lynch, J. And Lynch, J. 2003. Readers Guide to British History. Routledge.

McMahon, S. and McDonoghue, J. O. 2009. Brewers Dictionary of Irish Fable and Phrase. Chambers Harrap Publishers.

Jake Leigh-Howarth's picture


Jake Leigh-Howarth is a journalist and researcher from the UK with 8 years experience in music, travel, news, and historical journalism. He grew up in rural North Yorkshire where he developed a lifelong fascination for nature, mythology, folklore and history. ... Read More

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