The Uí Néill king Máel Sechnaill mac Domnaill, abandoned by his northern kinsmen of the Cenél nEógain and Cenél Conaill, acknowledged Brian as High King at Athlone in 1002. In the decade that followed, Brian campaigned against the northern Uí Néill, who refused to accept his claims, against Leinster, where resistance was frequent, and against Dublin. Brian's hard-won authority was seriously challenged in 1013 when his ally Máel Sechnaill was attacked by the Cenél nEógain king Flaithbertach Ua Néill, with the Ulstermen as his allies. This was followed by further attacks on Máel Sechnaill by the Norse Gaels of Dublin under their king Sihtric Silkbeard and the Leinstermen led by Máel Mórda mac Murchada. Brian campaigned against these enemies in 1013. In 1014, Brian's armies confronted the armies of Leinster and Dublin at Clontarf near Dublin on Good Friday. The resulting Battle of Clontarf was a bloody affair, with Brian, his son Murchad, and Máel Mórda among those killed. The list of the noble dead in the Annals of Ulster includes Irish kings, Norse Gaels, Scotsmen, and Scandinavians. The immediate beneficiary of the slaughter was Máel Sechnaill who resumed his interrupted reign as the last Uí Néill High King.
In death, Brian proved to be a greater figure than in life. The court of his great-grandson Muirchertach Ua Briain produced the Cogadh Gaedhel re Gallaibh, a work of near hagiography. The Norse Gaels and Scandinavians too produced works magnifying Brian, among these Njal's Saga, the Orkneyinga Saga, and the now-lost Brian's Saga. Brian's war against Máel Mórda and Sihtric was to be inextricably connected with his complicated marital relations, in particular his marriage to Gormlaith, Máel Mórda's sister and Sihtric's mother, who had been in turn the wife of Amlaíb Cuarán, king of Dublin and York, then of Máel Sechnaill, and finally of Brian.
The origin of his cognomen Boru or Borúma (of the tributes) is believed to relate to a crossing point on the river Shannon where a cattle-tribute was driven from his sept, the Dál gCais to the larger sept to which they owed allegiance, the Eóganachta. However, it seems more likely that he would have been given this name for being the man to reverse the tide of this tribute, and receive it back from those who his family formerly paid it to. Later legends originated to suggest that it was because he collected monies from the minor rulers of Ireland and used these to rebuild monasteries and libraries that had been destroyed during Norsemen (Viking) invasions.
An important influence upon the Dalcassians was the presence of the Hiberno-Norse city of Limerick on an isthmus around which the Shannon River winds (known today as King's Island or the Island Field). Undoubtedly the Hiberno-Norse of Limerick and the Dalcassians frequently came to blows, but it's unlikely that the relationship was always one of hostility; there was probably peaceful contact as well, such as trade. The Dalcassians may have benefited from these interactions, from which they would have been exposed to Norse innovations such as superior weapons and ship design, all factors that may have contributed to their growing power.
Brian immediately set about avenging his brother's death and reinstating the control of the Dalcassians over the province of Munster. In quick succession, he attacked and defeated the Hiberno-Norse of Limerick, Máel Muad's Irish allies, and finally, Máel Muad himself. Brian's approach to establishing his control over the Munster demonstrated features that would become characteristic of all of his wars: he seized the initiative, defeating his enemies before they could join forces to overwhelm him, and although he was ruthless and horribly brutal by modern standards, he sought reconciliation in the aftermath of victory rather than continuing hostility. After he had killed both the ruler of Limerick, Ivar, and Ivar's successor, he allowed the Hiberno-Norse in Limerick to remain in their settlement. After he had killed Máel Muad, he treated his son and successor, Cian, with great respect, giving Cian the hand of his daughter, Sadb in marriage. Cian remained a faithful ally for the rest of his life.
In 996 Brian finally managed to control the province of Leinster, which may have been what led Máel Sechnaill to reach a compromise with him in the following year. By recognising Brian's authority over Leth Moga, that is, the Southern Half, which included the Provinces of Munster and Leinster (and the Hiberno-Norse cities within them), Máel Sechnaill was simply accepting the reality that confronted him and retained control over Leth Cuinn, that is, the Northern Half, which consisted of the Provinces of Meath, Connacht, and Ulster.
Precisely because he had submitted to Brian's authority, the King of Leinster was overthrown in 998 and replaced by Máel Morda mac Murchada. Given the circumstances under which Máel Morda had been appointed, it is not surprising that he launched an open rebellion against Brian's authority. In response, Brian assembled the forces of the Province of Munster with the intention of laying siege to the Hiberno-Norse city of Dublin, which was ruled by Máel Morda's ally and cousin, Sigtrygg Silkbeard. Together Máel Morda and Sigtrygg determined to meet Brian's army in battle rather than risk a siege. Thus, in 999, the opposing armies fought the Battle of Glen Mama. The Irish annals all agree that this was a particularly fierce and bloody engagement, although claims that it lasted from morning until midnight, or that the combined Leinster-Dublin force lost 4,000 killed are open to question. In any case, Brian followed up his victory, as he and his brother had in the aftermath of the Battle of Sulchoid thirty-two years before, by capturing and sacking the enemy's city. Once again, however, Brian opted for reconciliation; he requested Sigtrygg to return and resume his position as ruler of Dublin, giving Sigtrygg the hand of one of his daughters in marriage, just as he had with the Eoganacht King, Cian. It may have been on this occasion that Brian married Sigtrygg's mother and Máel Morda's sister Gormflaith, the former wife of Máel Sechnaill.
The Annals state that, in the year 1002, Máel Sechnaill surrendered his title to Brian, although they do not say anything about how or why this came about. The Cogadh Gaedhil re Gallaibh provides a story in which Brian challenges High King Máel Sechnaill to a battle at the Hill of Tara in the province of Meath, but the High King requests a month long truce so that he can mobilise his forces, which Brian grants him. But Máel Sechnaill fails to rally the regional rulers who are nominally his subordinates by the time the deadline arrives, and he is forced to surrender his title to Brian. This explanation is hardly credible, given Brian's style of engaging in war; if he had found his opponent at a disadvantage he would certainly have taken full advantage of it rather than allowing his enemy the time to even the odds. Conversely, it is hard to believe, given the length and intensity of the struggle between Máel Sechnaill and Brian, that the High King would surrender his title without a fight.
Where that fight may have occurred and what the particular circumstances were surrounding it we may never know. What is certain is that in 1002 Brian became the new High King of Ireland.
Unlike some who had previously held the title, Brian intended to be High King in more than name only. To accomplish this he needed to impose his will upon the regional rulers of the only Province that did not already recognise his authority, Ulster. Ulster's geography presented a formidable challenge; there were three main routes by which an invading army could enter the Province, and all three favored the defenders. Brian first had to find a means of getting through or around these defensive 'choke points', and then he had to subdue the fiercely independent regional Kings of Ulster. It took Brian ten years of campaigning to achieve his goal which, considering he could and did call on all of the military forces of the rest of Ireland, indicates how formidable the Kings of Ulster were. Once again, it was his coordinated use of forces on land and at sea that allowed him to triumph; while the rulers of Ulster could bring the advance of Brian's army to a halt, they could not prevent his fleet from attacking the shores of their kingdoms. But gaining entry to the Province of Ulster brought him only halfway to his goal. Brian systematically defeated each of the regional rulers who defied him, forcing them to recognise him as their overlord.
Though it is only speculation, it has been suggested that Brian and the Church in Ireland were together seeking to establish a new form of kingship in Ireland, one that was modelled after the kingships of England and France, in which there were no lesser ranks of regional Kings – simply one King who had (or sought to have) power over all. In any case, whether as High King or Emperor, by 1011 all of the regional rulers in Ireland acknowledged Brian's authority. Unfortunately, no sooner had this been achieved than it was lost again.
Máel Mórda mac Murchada of Leinster had only accepted Brian's authority grudgingly and in 1012 rose in rebellion. The Cogadh Gaedhil re Gallaibh relates a story in which one of Brian's sons insults Máel Morda, which leads him to declare his independence from Brian's authority. Whatever the actual reason was, Máel Morda sought allies with which to defy the High-King. He found one in a regional ruler in Ulster who had only recently submitted to Brian. Together they attacked the Province of Meath, where the former High King Máel Sechnaill sought Brian's help to defend his Kingdom. In 1013 Brian led a force from his own Province of Munster and from southern Connacht into Leinster; a detachment under his son, Murchad, ravaged the southern half of the Province of Leinster for three months. The forces under Murchad and Brian were reunited on 9 September outside the walls of Dublin. The city was blockaded, but it was the High King's army that ran out of supplies first, so that Brian was forced to abandon the siege and return to Munster around the time of Christmas.
Máel Morda may have hoped that by defying Brian, he could enlist the aid of all the other regional rulers Brian had forced to submit to him. If so, he must have been sorely disappointed; while the entire Province of Ulster and most of the Province of Connacht failed to provide the High King with troops, they did not, with the exception of a single ruler in Ulster, provide support for Máel Morda either. His inability to obtain troops from any rulers in Ireland, along with his awareness that he would need them when the High King returned in 1014, may explain why Máel Morda sought to obtain troops from rulers outside of Ireland. He instructed his subordinate and cousin, Sigtrygg, the ruler of Dublin, to travel overseas to enlist aid.
Sigtrygg sailed to Orkney, and on his return stopped at the Isle of Man. These islands had been seized by the Vikings long before and the Hiberno-Norse had close ties with Orkney and the Isle of Man. There was even a precedent for employing Norsemen from the isles; they had been used by Sigtrygg's father, Amlaíb Cuarán, in 980, and by Sigtrygg himself in 990. Their incentive was loot, not land. Contrary to the assertions made in the Cogadh Gaedhil re Gallaibh, this was not an attempt by the Vikings to reconquer Ireland. All of the Norsemen, both the Norse-Gaels of Dublin and the Norsemen from the Isles, were in the service of Máel Morda. It should also be remembered that the High King had 'Vikings' in his army as well; mainly the Hiberno-Norse of Limerick (and probably those of Waterford, Wexford, and Cork as well), but also, according to some sources, a rival gang of Norse mercenaries from the Isle of Man.
Essentially this could be characterised as an Irish civil war in which foreigners participated as minor players.
Along with whatever troops he obtained from abroad, the forces that Brian mustered included the troops of his home Province of Munster, those of Southern Connacht, and the men of the Province of Meath, the latter commanded by his old rival Máel Sechnaill mac Domnaill. He may have outnumbered Máel Morda's army, since Brian felt secure enough to dispatch a mounted detachment under the command of his youngest son, Donnchad, to raid southern Leinster, presumably hoping to force Máel Morda to release his contingents from there to return to defend their homes. Unfortunately for the High King, if he had had a superiority in numbers it was soon lost. A disagreement with the King of Meath resulted in Máel Sechnaill withdrawing his support (Brian sent a messenger to find Donnchad and ask him to return with his detachment, but the call for help came too late). To compound his problems, the Norse contingents, led by Sigurd Hlodvirsson, Earl of Orkney and Brodir of the Isle of Man, arrived on Palm Sunday, 18 April. The battle would occur five days later, on Good Friday.
The fighting took place just north of the city of Dublin, at Clontarf (now a prosperous suburb). It may well be that the two sides were evenly matched, as all of the accounts state that the Battle of Clontarf lasted all day. Although this may be an exaggeration, it does suggest that it was a long, drawn-out fight.
There are many legends concerning how Brian was killed, from dying in a heroic man-to-man combat to being killed by the fleeing Viking mercenary Brodir while praying in his tent. He is said to be buried in the grounds of St. Patrick's Cathedral in the city of Armagh. Legend dictates he is buried at the north end of the church.
The influence of this work, on both scholarly and popular authors, cannot be exaggerated. Until the 1970s most scholarly writing concerning the Vikings' activities in Ireland, as well as the career of Brian Boru, accepted the claims of Cogadh Gaedhil re Gallaibh at face value.
Brian did not free Ireland from a Norse (Viking) occupation simply because it was never conquered by the Vikings. In the last decade of the 8th century, Norse raiders began attacking targets in Ireland and, beginning in the mid-9th century, these raiders established the fortified camps that later grew into Ireland's first cities: Dublin, Limerick, Waterford, Wexford, and Cork. Within only a few generations, the Norse citizens of these cities had converted to Christianity, inter-married with the Irish, and often adopted the Irish language, dress and customs; thus becoming what historians refer to as the 'Hiberno-Norse'. Such Hiberno-Norse cities were fully integrated into the political scene in Ireland, long before the birth of Brian. They often suffered attacks from Irish rulers, and made alliances with others, though ultimately came under the control of the kings of the Provinces of Meath, Leinster, or Munster, who chose those among Hiberno-Norse who would rule the cities, subservient to their loyal subordinates. Rather than conquering Ireland, the Vikings, who initially attacked and subsequently settled in Ireland were, in fact, assimilated by the Irish.
According to Njal's Saga, he also had a foster-son named Kerthialfad.
The website for Irish vodka brand Boru says it is "named for the legendary king Brian Boru, who united Ireland in 1014.
Celtic metal band Mael Mórdha derived their name from the king of Leinster who fought against Brian. This was also the theme of their 2005 debut album Cluain Tarbh. Another Celtic metal band Cruachan has used the story of Brian Boru for a song "Ard Rí Na hÉireann" (translated as "The High King of Ireland") on their 2004 album Pagan.
His name is remembered in the title of one of the oldest tunes in Ireland's traditional repertoire : Brian Boru's March. Which is still widely played by traditional Irish musicians. French Breton singer Alan Stivell released in 1995 an album called Brian Boru. Most notable for a pop song reprise of the March (though the tune is normally an instrumental piece)
In "Strapping Young Lads" by Brian Dunning, Brunnhilde claimed to have killed Boru in single combat, and "torn his still-beating heart from his breast."
Limerick band Lucky Numbers released their hit single Brian Boru in 1979.
Robert E. Howard mentions Brian Boru and the Battle of Clontarf in a Turlogh Dubh O'Brien story, The Dark Man. Turlogh wears a torc given to him by the High King before that battle. He also wrote a fictionalised account of the battle in his story The Twilight of the Grey Gods.
Intrigue, Magic, Rebels and Royalty: A Battle for the Ages ; Why Do Brian Boru and the Battle of Clontarf Have Such an Enduring Role in Irish History?
Jun 04, 2013; April 23rd, 2014, will be the 1,000th anniversary of the Battle of Clontarf. This major battle is probably the best known event...