On Good Friday, April 23, 1014 just north of Dublin a momentous and bloody battle was fought. At stake was the nascent unification of the island under its first true king, Brian Boru; and the future influence of the Vikings, who had settled and meddled in Ireland for nearly two centuries. The battle that resulted changed the course of Irish history forever!
The Vikings first began raiding Ireland in the late 8th century. As throughout western Europe, longships crammed with veteran warriors bent on rapine and plunder descended on the coastal settlements and raided deep into the countryside; bringing death and destruction to the unwary inhabitants. These Vikings were perhaps the first iron-clad, mailed warriors the Irish had ever encountered: the defending Gaelic warriors “had nothing to defend their bodies… save only elegant tunics, shields, and finely wrought collars”; who fought as light infantry in loose-formation. By contrast, the Vikings were often veteran warriors, who fought in close order, “a solid, skillful, and firm rampart of strong coats of mail like a thick, dark stronghold of black iron with a battle-wall of gleaming shields around their chiefs”
Ireland was a divided land, made up of warring clans and kingdoms, ruled by some 150 different petty kings. Though there was a High King who in theory exercised a position as primus inter pares (first among equals) over the other petty kings, his authority depended solely on the strength of his personality and the number of swords whose loyalty he could command. In a land so divided, a relatively small numbers of aggressive Vikings were able to work great mischief, taking advantage of the lack of central authority and playing one Irish petty king against another. Norse settlements and fortified bases (longphorts) soon dotted the coasts and major river-ways. Limerick, Cork, Waterford, Wexford, and Dublin all began as Norse (or Danish) settlements.
The Scandinavians came to Ireland not only as merciless Viking raiders; but as settlers, founding towns and trade centers along the coast and inland waterways. The greatest of these settlements, Dublin, is today Ireland’s national capital.
Most of those who first raided Ireland were Norsemen (from Norway), who the Irish called the fionngaill (“fair strangers”), to distinguish them from the other nation of Vikings, the Danes or dubhgaill (“dark strangers”)*. The first great Viking lord in Ireland was Turgeis (Thorgis?). He arrived in 839, leading “a great sea-cast flood of foreigners into Eire, so that there was not a point (along the coast) thereof without a (Viking) fleet”. Turgeis raided deep into Ireland, attacking the chief religious center of the land, Armagh; where he drove out the Bishop, who fled with relics of St. Patrick. Turgeis established himself as lord of Dublin (the “Dark Pool”); previously a Christian ecclesiastical settlement but now a Norse military settlement. Dublin was perfectly situated at a ford of the River Liffey, and possessed of a fine harbor for trade and the anchorage of Viking longships.
Raging through the heart of Ireland, Turgeis took the monastery of Clonmacnoise; and placed his wife, Ota, in control. There she sat as a pagan priestess (völva or spækona), holding court and giving oracles from the high alter. Turgeis’ colorful career as Viking conquistador was short-lived, however. According to the Annals of Ulster he was captured in 845 by the Irish, and drowned in Lough Owel.
However, his place as leader of the fionngaill in Ireland and king of Dublin was taken in 853 by a Irish-born Norseman, Olaf the White. Olaf shared the rule of Dublin and leadership of the Hiberno-Norse community with another Viking leader who arrived in Ireland around 870, Ímar (also rendered as Imhar in Irish sources). This latter’s identity is a source of controversy, but some think him identical with the famed Ivar the Boneless, son of the legendary Viking leader Ragnar Lothbrok; and sometime commander (along with his brothers) of the Great Heathen Army that invaded and overran much of England between 865 and 878. Mention of Ivar as leader of the Great Heathen Army in England disappears from the record in 870, so it is theorized that he came to Ireland to take over leadership of Dublin. The connection between the Irish-Viking Ímar and Ivar the Boneless is not certain, but whoever he was Ímar/Ivar founded a royal line in Ireland: the Uí Ímair, or House of Ivar. This house ruled (at various times) much of the Irish Sea region, the Kingdom of Dublin, the western coast of Scotland, the Hebrides and some part of northern England (including York), from the mid 9th century till the 11th.
In the shifting landscape of Irish politics, these Hiberno-Norse soon became part of the regular fabric of intrigues and alliances; siding with one or another of the native petty kings in the island’s ceaseless internecine conflicts. So long as the Irish were divided, the presence of the “Lochlannach” would have to be tolerated till the arrival of a king strong enough to drive them out.
In the latter half of the 10th century, just such a warlord arose.
In 868 an obscure western Irish tribe, the Dál Cais, rose up under two brothers, Mahon and Brian mac Cennétig (sons of Kennedy) to oppose the Lochlannach in Munster. The brothers defeated the powerful Viking lord of Limerick, Ivar (a descendant of the founder of the Uí Ímair) at the Battle of Selcoit. The brothers followed up their victory by sacking Limerick, wealthy stronghold of the Vikings on the River Shannon.
Irish warriors traditionally wore little armor, in contrast to the Viking invaders.
Following this victory, these two Dalcassian brothers spent the next eight years fighting rivals for the lordship of Munster. In 976 Mahon was captured and executed by a Gaelic rival. Brian, who had been his brother’s commander, now took over the lordship of the Dal Cais. In two years, he avenged his brother’s murder at the Battle of Belach Lechta, in which his rival was slain and he assumed the title of King of Munster.
Thus began the career of Brian Boru (Bóruma), and his march along the path to greatness. For the next few years, he extended his influence into the neighboring kingdoms of Leinster to the east and Connacht to the north. This brought him into conflict with Ireland’s most powerful lord, Máel Sechnaill mac Domnaill (anglicized and refered to further as Malachi), “Ard Rí“ (High King) of Ireland and ruler of Meath. From 982 to 997 these two powerful kings engaged in a war for primacy. During these campaigns, Brian proved a highly able strategist; utilizing both land and naval forces to achieve his ends. By 996 he had all-but conquered Leinster; and the following year n 997, at a royal meeting near Clonfert, Malachi and Brian made a truce. The terms granted Brian rule over the southern half of Ireland; while Malachi retained the northern half and the title of High King.
The Leinstermen chaffed at being under the dominance of Munster; and within two years were in open revolt. Máel Mórda, king of the Uí Fáeláin of northern Leinster, joined forces with his maternal uncle, Sitric Silkbeard, king of Dublin. First they turned upon and defeated Brian’s vassal, Donnchad mac Domhnaill, the King of Leinster, and imprisoned him in Dublin. Máel Mórda claimed his title; and Dublin and Leinster now defied both Brian and Malachi of Meath. Brian and Malachi marched against the rebels, defeating them decisively at the bloody Battle of Glenmama , on December 30, 999. As the rebel army fled the field, many were slaughtered as Brian’s forces closely pursued. Máel Mórda allegedly survived the rout by hiding in a yew tree. To his enduring shame, he was dragged from its branches by Brian’s eldest son, the redoubtable Prince Murrogh (often rendered as Murchad); and taken captive. Sitric survived the battle and temporarily left Ireland. His brother, Harald Olafsson, was not so lucky; being one of some 7,000 to fall in the battle or the pursuit.
The following day, New Years Eve, 999, Brian’s army reached Dublin. They entered the undefended town; and on New Year’s Day, 1000 Viking Dublin was sacked by Brian’s army. A great trading port, the plunder was rich indeed.
Brian stayed in Dublin for several months, settling affairs. Donnchad mac Domhnaill was freed and returned to the throne of Leinster (though he would be found an unsatisfactory client; and would be deposed a few years later; and Máel Mórda, swearing loyalty, was placed on the Leinster throne). Sitric returned, after raiding in Wales, and was reinstated as king of Dublin. To seal the peace between he and his new overlord, he was given Brian’s daughter Sláine to wife. King Brian, in turn, was wed to Sitric’s still-lovely and passionate mother, Gormlaith (called Kormlada in Icelandic sources). Sister to Máel Mórda, she had been married twice before: to Sitric’s father, the powerful Viking king of Dublin and York, Olaf Cuaran; and, more recently, Brian’s erstwhile rival-turned-ally, Malachi of Meath. Divorced from the latter, she was now bride to the most powerful warlord in Ireland.
The victory of Glenmama and capture of Dublin put Brian in an unprecedented seat. Never before had an Irish king been in the position of direct overlord of that city’s Viking king. In bestowing it upon Sitric (scion of the Uí Ímair, rulers of Dublin since Ivar the Boneless) Brian had now set a precedent: that “the city’s Hiberno-Scandinavian ruler would hold his kingship from his Munster overlord”, a vassal lord, no longer independent. As for Brian Boru he was indisputably the strongest warlord in Ireland; eclipsing the power of his ally, Malachi of Meath, the High King.
In the following year, the arrangement between these two paramount kings and rivals broke down. His ambitions perhaps now goaded on by his new bride (Malachi’s ex-wife) Gormlaith, Brian marched against Malachi in the north. Despite setbacks, Brian was eventually successful. In 1002, Malachi surrendered his title of “Ard Rí“, High King, to Brian. Unlike those who had held this title before him, Brian was unwilling to be merely “first among equals”; but instead to rule in fact as well as name. Continuing his military activities in the far north of the island, over the next nine years Brian systematically brought the proud Uí Néill of Ulster to heal. By 1011, he was acknowledged by all the rulers of Ireland as their overlord.
Brian Boru was Ireland’s first true “king”. More, he was acknowledged by the highest religious authority in Ireland, the monastery of Armagh, as not just king, but Imperator Scottorum: “Emperor of the Irish”. 
But his position, so unique in Irish history, did not long go unchallenged.
REVOLT IN LEINSTER
Though he owed his throne to Brian, Máel Mórda of Leinster resented his brother-in-law’s dominance. His loyalty, of thin tissue to begin with, must have been further strained when Brian put off his wife, Gormlaith, Máel Mórda’s sister. When his divorce from Gormlaith occurred is unknown; nor is the reason. But by 1011 she was back with her brother, bitter towards her (ex?) husband. Her spite would play a key role in the events that led to Clontarf.
While visiting Brian’s court at Kincora, Máel Mórda was observing a chess game; between Brian’s eldest son, Murrogh, and his cousin Conaing. The Leinster King advised the latter on a move. Prince Murrogh, tactlessly, reminded Máel Mórda that his advice before Glenmama had not been so sound; and further teased him about having been pulled from a tree after the battle. This insult was a goad no warrior would bear.
A furious Máel Mórda stormed off, leaving the palace and riding for home; without a word of leave to King Brian. Hearing of this, Brian sent a messenger to follow and bring Máel Mórda back. The Leinster king killed Brian’s messenger and rode on. Retribution was now inevitable.
Back in own palace at Cill Chuilinn (modern Kilcullen) in Leinster, Máel Mórda might have reconsidered, given time to cool off; were it not for Gormlaith. Handing his sister the tunic he had worn at Kincora, he asked her to sew on a button that had fallen off. Gormlaith took the tunic, and threw it into the fire. She then scornfully upbraided him, that he should take his kingship in vassalage of another (Brian); something their father and ancestors had never done! She reminded him that one day, perhaps soon, he would have to bend the knee to Brian’s son-and-heir, Murrogh; the very man who had so insulted him.
Máel Mórda now resolved to rebel. He went with Gormlaith to Dublin, where they incited her son, Sitric Silkybeard to join them. The two joined forces for a second time, and spent 1013 raiding into Brian and Malachi’s territory. Brian responded by marching on Leinster and Dublin; Brian and Murrogh approaching by two different routes, ravaging their enemies territory as they advanced. In September, 1013, Brian’s army encamped at Kilmainham (now a suburb of Dublin), a mile from city; intending to blockade the land approaches to Dublin and starve the town into submission. But the attempt was unsuccessful, for the town could re-provision by sea. Brian’s army ran short of supplies first, and the High King was forced to withdraw before Christmas.
The rebels knew Brian would return again in the spring, and so undertook measures to strengthen their position. They sent to other disaffected princes, several of whom promised aid. But Dublin had been badly weakened by the defeat of Glenmama. To strengthen their numbers and aid their cause, they needed help from outside Ireland. Gormlaith convinced her son to take ship; and travel to the north of Scotland; where such help could be found.
In Orkney, Sitric met with the mightiest Viking warlord in the Western Islands, Sigurd the Stout, Jarl of the Orkneys. It was Yule, and Sitric joined the Orkney Jarl in feasting and celebration (recounted in Njals Saga). After which, the two made a pact: For his aid, Sitric promised Sigurd lordship of Ireland, once they defeated Brian. More: his mother Gormlaith (despite her age, still a great beauty) would be given Sigurd for wife.
It was in a Viking Mead Hall like this that Jarl Sigurd feasted King Sitric over Yule, 1013.
It should be remembered that events in Ireland did not exist in a vacuum. In neighboring England, Sveinn Forkbeard, King of Denmark, had invaded with a large army and driven King Æthelred the Unready, descendant of Alfred the Great, from his throne. On Christmas Day 1013, while Sitric and Sigurd feasted in Orkney, Sveinn Forkbeard was crowned King of England as well as Denmark.
Across the north, Viking leaders like Sigurd took note: What such great Viking chieftains as Turgeis, Ivar the Boneless, and Olaf Cuaran had dreamed of seemed now, at last, within reach to any strong and bold enough to grasp it. Their star was ascendant; the day of the Northmen had come. What Sveinn Forkbeard had achieved in mighty England, could not Sigurd the Stout do in Ireland? Brian was an old man (chroniclers put his age at between 72 and 88 at Clontarf). Perhaps it was time to topple the “Emperor of the Irish” from this throne, and a Northman take his place.
Sigurd promised to be at Dublin with all his strength by Palm Sunday, 1014.
Standing Stones at Orkney, stronghold of Jarl Sigurd the Stout.
With the Orkney Jarl’s pledge in hand, Sitric returned to Dublin. But when he conferred with his mother, Gormlaith, she was still not satisfied that he had sufficient allies to challenge Brian in battle. She told him that a fleet of 30 longships lay off the Island of Man. There, he should seek the alliance of the two fierce Viking warlords who commanded this force, and offer them whatever it took to gain their aid.
* The Scandinavian element within Ireland in this period is sometimes referred to as Hiberno-Norse; or Hiberno-Scandinavian. Those of Dublin are referred to, alternately as Dublin-Norse, or Dublin-Danes. All of these are, to an extent, correct. There were both Danish and Norse settlers in Ireland; and the population of Dublin was very mixed. Though kingship changed hands from time-to-time in Dublin between various Viking leaders, the House of Ivar (Uí Ímair), which ruled Dublin for most of the Viking Age, may have descended from Ivar the Boneless; who was certainly a Dane. So Dublin-Dane is perhaps the most correct for the Vikings of Dublin. When referring to the Scandinavian element in Ireland as a whole, whether Hiberno-Scandinavian settlers or “foreign” contingents, I shall herein use the catch-term “Viking”. Though not strictly correct (“Viking” means pirate or raider; and not all Scandinavian’s in Ireland at this time engaged in such activities), it will serve, for clarity’s sake.
 Ailbhe Mac Shamhráin, The Battle of Glenn Mama, Dublin and the High Kingship of Ireland: a Millennial Commemoration; (Medieval Dublin, edited by Sean Duffy, 2001 pp53-64).
 “Scottorum” was the Latin term for the Irish. Ireland was usually referred to in Latin as “Scotia Major”; while Scotland was referred to as “Scotia Minor”.
 After his brother detached a third of their fleet and sailed off to join Brian, the remaining two-thirds still under Brodir’s command, and which he brought to Clontarf, numbered 1,000. So one can infer from this that the combined host at Man numbered 1,500; with an average of 50 men per longship.
Some of the artwork in this article has been reproduced with the permission of Osprey Publishing, and is © Osprey Publishing, part of Bloomsbury Publishing Plc.