Muirchertach Ua Briain (anglicised as Murtaugh O'Brien; – , son of Toirdelbach Ua Briain and great-grandson of Brian Boru, was King of Munster and later self-declared High King of Ireland.
Background and early career
Muirchertach Ua Briain was a son of Toirdelbach Ua Briain, the previous Dalcassian King of Munster and de facto High King of Ireland. As a descendant of Brian Boru, he was part of the powerful O'Brien dynasty who ruled Ireland at the time. His mother was Derbforgaill, daughter of Tadhg Mac Giolla Pádraig of Osraige, who also bore Muirchertach's brother Tadhg.Carrigan; History and Antiquities of the Diocese of Ossory, vol. 1, pg 51.
His early life is largely unknown. The Annals of Tigernach give his birth date as 1050. Afterwards, he is not mentioned in any of the annals of Ireland until the year 1075 when he was defeated by the Kingdom of Airgíalla in battle near modern Ardee in County Louth, taking heavy losses. This was part of a series of campaigns undertaken by his father Toirdelbach against rebellious lesser kings in the north of the country. He was later appointed as king or governor of the city-state of Dublin by his father.https://www.academia.edu/29536360/Muirchertach_Ua_Briain_politics_and_naval_activity_in_the_Irish_Sea_1075_to_1119 Candon, Anthony "Muircherteach Ua Briain, politics and naval activity in the Irish sea, 1075-1119." pages 1–5
Governor of Dublin Background: Importance of Dublin
Despite the victory of Muirchertach's great-grandfather Brian Boru over the Vikings at the Battle of Clontarf in 1014 and the breaking of Norse power in Ireland, Dublin remained under the rule of Norse–Gael kings and had links with other Viking Kingdoms. They paid tribute to their Irish overlords, but otherwise the Irish rarely interfered, mainly because of the trade the Norse brought to the area.
However, in 1052, the King of Dublin, Echmarchach mac Ragnaill, was removed by the King of Laigin (Leinster), Diarmuit mac Maíl ma mBó. Echmarchach was replaced by Diarmuit's son, Murchad. As a prince of Leinster, Murchad acted as a sort of governor of the city on behalf of his father, the King. Diarmuit seemed to appreciate the importance of Dublin which, even back then, was recognised as a sort of national capital city and was important for a number of reasons, including trade and its military forces, particularly its navy.
Appointment of Muirchertach
Following the death of the King of Leinster in the year 1075, Dublin came under the control of Muirchertach's father, Toirdelbach mac Tadhg Ua Briain, King of Munster and High King of Ireland, as he expanded his power throughout Ireland. Toirdelbach at first appointed Godfraid mac Ragnaill as king but he was later expelled by Toirdelbhach. He then placed a man by the name of Domnall as governor but he was himself replaced by Muirchertach later that same year after the former's sudden death. This was probably Muirchertach's first major political appointment as it was in this year that he was first mentioned in the Annals of Tigernach, signifying the power and the importance of the position he held.
As governor, he would have had frequent contact with the Archbishop of Dublin, Patrick. Patrick had previously held various positions within the Catholic Church in England and would have been very familiar with the politics of England following the Norman Conquest in 1066. Patrick possibly influenced Muirchertach's great interest in affairs outside Ireland later in his career.
On 19 October 1084, Muirchertach led a large army consisting of the armies of the Kingdoms of Dublin, Leinster, Osraige and Munster against the forces of Donchad ua Ruairc of Breifne, in a battle at Moin Croinnioce, near modern Leixlip in County Kildare. Over 4,000 men were killed in the battle, with Muirchertach heavily defeating the forces of Ua Ruairc. After the battle, Muirchertach cut off Ua Ruairc's head and brought it to his father's palace in Kincora.
King of Munster In 1086, following the death of his father Toirdelbach, Muirchertach claimed the Kingship of Munster. Initially, Toirdelbach had divided the Kingdom among his three sons Muirchertach, Diarmuit and Tadc. However, Tadc died the following year and Muirchertach banished Diarmuit, claiming the entire province for himself. Diarmuit, however, was evidently not going to let Muirchertach take the Kingship so easily and made an alliance with the King of Leinster. The forces of Diarmuit and Leinster met with the forces of Muirchertach at Raith Etair, possibly the promontory fort on Howth Head in northern County Dublin. The forces of Muirchertach were victorious, and Muirchertach's claim to the Kingship was no longer under any threat.
In 1088, Muirchertach led a number of naval campaigns against Ruadhrí na Saide Buide Ua Conchobhair, King of Connacht. The first fleet sailed up the River Shannon as far as Clonfert, but the crews were slaughtered by the Connachtmen. Another fleet was sent around the western coast of Ireland on the Atlantic Ocean, but this fleet was also defeated by the forces of Connacht. Ruadhrí then attacked Munster when he invaded northern County Clare, near the homeland of the Dál gCáis.
However, a new rival emerged in the form of Domnall Mac Lochlainn, King of the Northern Uí Néill, who later in 1088 invaded Connacht and successfully gained the submission of Ruadhrí na Saide. Ruadhrí and Domnall formed an alliance and together they attacked Munster. At the time, Muirchertach was away campaigning in Leinster. They burned and looted Limerick, Killaloe and Emly, and took over 160 hostages. Muirchertach was forced to buy back these hostages with gold, silver, cattle and meat.
According to a source from Munster, Muirchertach avenged himself by attacking the Kingdoms of Meath and Leinster, the latter presumably having fallen into enemy hands since the time Muirchertach had been governor of Dublin. He gained the submission of both provinces, killing the King of Leinster in the process. He also fought around Dublin, burning a building in Lusk, County Dublin killing over 160 people inside. He then headed west and cut down the sacred inaugural tree of the Kings of Connacht. Muirchertach was involved in further naval actions against Connacht the next year in 1089 when he was looting islands in Lough Ree, but Ruadhrí na Saide blocked the path home on the River Shannon around the settlement of Clonmacnaoise, forcing Muirchertach to hand over his ships to the forces of the Kingdom of Meath after retreating to Athlone. He marched with his army back home to Munster on foot, but using Muirchertach's confiscated ships, the Meathmen and Connachtmen sailed southward on the Shannon and plundered the plains around Cashel.
Four kings now battled for supremacy in Ireland: Muirchertach Ua Briain of the Kingdom of Munster, Domnall Ua Maél Sechnaill of the Kingdom of Mide, Ruadhrí na Saide Buide Ua Conchobhair of the Kingdom of Connacht, and Domnall Mac Lochlainn of the Northern Uí Néill. The four kings met in 1090, where Mac Lochlainn was acknowledged as High King of Ireland and he received hostages from the other three kings. Following this conference, Muirchertach went on campaign in Leinster again, but while he was away, Munster was attacked by Ua Maél Sechnaill who was joined by Ruadhrí na Saide. Although he was defeated by the Meath forces, he was able to drive the armies of Connacht back, and then received assistance from Mac Lochlainn in the north in defeating Ua Maél Sechnaill.
Ruadhrí na Saide again invaded Munster two years later in 1091, but he was blinded the following year in 1092 by Flaithbertaigh Ua Flaithbertaigh, throwing the Kingdom of Connacht into a state of political turmoil. Muirchertach took advantage of this situation by invading the province and gaining the kingship, in the process possibly taking in and grooming his nephew Tairrdelbach Ua Conchobhair for the day he would become king of Connacht. These events left Muirchertach in the south and Mac Lochlainn in the north the most powerful kings in Ireland. He continued expanding his power with further campaigns in Mide, more or less gaining the overlordship of the region, and he reconciled with his brother Diarmuit at Cashel in 1093.Annals of the Four Masters, UCC Corpus of Electronic Texts (CELT) version, Part 22, accessed 21 April 2008
King of Ireland In 1094, Muirchertach fought the kings of Leth Cuinn and Gofraid Crobán, King of Dublin and the Isles. He went with his army to Dublin and banished Gofraid, and brought about the killing of Domnall Ua Maíl Shechnaill. He asserted supremacy over the Southern Uí Néill of the Kingdom of Meath, dividing the province between two rival clans, applying a policy of divide and rule, which had been used very effectively by his father before him.
The Irish Sea and Magnus Barefoot
Since the Kingdom of Dublin had fallen to the Irish of Leinster in the year 1052, Irish influence in the Irish Sea, particularly the Kingdom of Man and the Isles, had greatly increased. Diarmuit mac Maíl na mBó, King of Leinster and High King of Ireland, was also King of the Isles through capturing Dublin as Dublin was part of this Kingdom. Having ousted the Norse–Gael king, he was in a very powerful position. After Diarmuit's death, Muirchertach's father, Toirdelbach, became High King of Ireland and had control of Dublin. He was involved in the Isle of Man as well, more or less controlling the island, possibly through one his sons, Tadc, brother of Muirchertach, marrying a woman from the Manx royalty.
Upon Toirdelbhach's death and the accession of Muirchertach to the throne, the Manx may have used the opportunity to assert some form of independence from Irish rule, lasting until 1095, when Muirchertach was able to assert control, again through a political marriage into Manx Royalty, who had requested a king from the Irish royal bloodline. This time, the alliance was made through his nephew Diarmuit, Tadc's son, who married a Manx princess. By gaining overlordship of the Isles, Muirchertach was able to access the manpower and large naval fleets of the Isles, and he had a base from which to launch assaults on Ulster in the Hebrides, which would prove useful in his war against Domnall Ua Lochlainn.
However, this attracted the attention of the King of Norway, Magnus III, better known as Magnus Barefoot, who wanted to retain Norwegian power in the area and bring the Norse Kingdoms such as Orkney, the Isles and Dublin. With a fleet of around sixty ships and several thousand men, he re-established Norse power in the area, garrisoning the islands of Orkney and Man. Although some sources say he did want to conquer Ireland, there was not much contact between the Norwegians and the Irish, apart from an incident when three Norwegian ships were sunk by the Ulaid (who were under Muirchertach's overlordship), probably while cattle raiding in the area. Some sources do say Magnus planned a full assault on Ireland, but the Irish gathered a large army on the coast, and Magnus did not attack.
Earlier, Muirchertach had sent a fleet to Wales to help the Welsh fight the Normans who were encroaching on their territory on the island of Anglesey. However, the Normans were able to buy off the Irish ships to their side, and the Welsh were defeated. The Norman victory celebrations were interrupted by Magnus, however, who landed and routed the Norman army, reputedly shooting Hugh de Montgomery, brother of Arnulf, through the eye. Later, when the Irish fleet returned home, they were punished by Muirchertach for their treachery. After this event, Anglesey was considered the southernmost point of the Kingdom of Norway. After these campaigns, Magnus went home to Norway to campaign against Sweden, but he would return later.