Battle of Glenmama

The Battle of Glenn Máma (Cath Ghleann Máma, The Battle of "The Glen of the Gap" ) or Glenmama was a battle that took place in County Wicklow in AD 999. It was the decisive and only engagement of the brief Leinster revolt of 999–1000 against the King of Munster, Brian Boru. In it, the combined forces of the Kingdoms of Munster and Meath, under King Brian Boru and the High King of Ireland, Máel Sechnaill II, inflicted a crushing defeat on the allied armies of Leinster and Dublin, led by King Máel Mórda of Leinster.

The two armies met in a narrow valley in the Wicklow Mountains, causing a rout of Máel Mórda's army in at least three directions. They were pursued, and the main body of the army was slaughtered when they rallied at several fording points along the River Liffey. The main commanders were either killed or captured.

The battle resulted in the occupation of Dublin by Brian's Munster forces, and the submission of Máel Mórda and King Sigtrygg Silkbeard of Dublin to Brian Boru. The solution did not prove permanent, however, and eventually resulted in the second Leinster revolt against Brian and the Battle of Clontarf in 1014.

Background
In 997, at a royal meeting near Clonfert, Brian Boru, King of Munster, met with his long-time rival Máel Sechnaill mac Domnaill, who was at the time High King of Ireland. Although the idea of the high-kingship is considered mainly an anachronistic invention, it came into vogue in the 10th century to denote a king who had enforced his power over external territories. Máel Sechnaill assumed the Irish high-kingship after the Battle of Tara in 980.

The two kings made a truce, by which Brian was granted rule over the southern half of Ireland, while Máel Sechnaill retained the northern half and high kingship. In honour of this arrangement, Máel Sechnaill handed over to Brian the hostages he had taken from Dublin and Leinster; and in 998, Brian handed over to Máel Sechnaill the hostages of Connacht. In the same year, Brian and Máel Sechnaill began co-operating against the Norse of Dublin for the first time.

Late in 999, however, the Leinstermen, historically hostile to domination by either the Uí Néill overkings or the King of Munster, allied themselves with the Norse of Dublin and revolted against Brian. According to the 17th century Annals of the Four Masters, the following prophecy had predicted the Battle of Glenmama:

"They shall come to Gleann-Mama, It will not be water over hands, Persons shall drink a deadly draught Around the stone at Claen-Conghair. From the victorious overthrow they shall retreat, Till they reach past the wood northwards, And Ath-cliath the fair shall be burned, After the ravaging the Leinster plain."

Battle
The Annals of the Four Masters records that Brian and Máel Sechnaill united their forces, and according to the Annals of Ulster, they met the Leinster-Dublin army at Glenmama on Thursday, 30 December 999. Glenmama, near Lyons Hill in County Kildare, was the ancient stronghold of the Kings of Leinster. According to the 170-year-old theory of Shearman, there was a valley that divided a sub-range to the Wicklow Mountains. The southern ridge faces the modern town of Dunlavin, but recent scholarship has resited the battle on the approaches to Dublin city on the Dublin-Kildare border.

"It would appear that the Norse expected to reach Dunlavin, and perhaps to encamp there to meet the forces of Meath and Munster." It seemed to Shearman that Brian had anticipated their movements, and cut off their retreat "in the narrow defile" of Glenmama. With no room for a regular encounter, the flight of the Danish army must have begun immediately. The main body of the army rallied at the ford of Lemmonstown, where thousands were said to have fallen. The remnant of the defeated army fled about a mile east of the ford to Hollywood, and were utterly routed at the ford of the Horsepass on the River Liffey.

A smaller body of cavalry fled through Glanvigha, possibly to reach the ford of the Liffey at Ballymore Eustace, and some of them perished crossing the morass in Tubber. A third party fled from the valley eastward to the Bealach Dunbolg to "the shelter of the wild recesses of Hollywood and Slieve Gadoe". Brian pursued them, and his son Murchad allegedly pulled Máel Mórda from the tree in which he was hiding.

The Munster-Meath army defeated the Leinster-Dublin army; according to the propagandist Cogadh Gaedhel, the battle was "bloody, furious, red, valiant, heroic, manly; rough, cruel and heartless;" and that there had been no greater slaughter since the 7th century Battle of Magh Rath. Later historians have also seen the battle as decisive. Ó Corráin refers to it as a "crushing defeat" of Leinster and Dublin, while The dictionary of English history says the battle effectively "quelled" the "desperate revolt" of Leinster and Dublin. Tradition records that "the son of the King of the Danes", Harold Olafsson, was killed in the retreat, and was interned at the now obscure cemetery of Cryhelpe. Brian took Máel Mórda of Leinster prisoner and held him until he received hostages from the Leinstermen. It was alleged that 7000 Norse fell in the battle. This was at a time when warfare was fought on a very limited scale, and raiding armies generally had between a hundred and two hundred men. Most importantly, the defeat left the road to Dublin "free and unimpeded for the victorious legions of Brian and Maelsechlainn".

Aftermath
The victory was followed up with an attack on the city of Dublin. The 12th century Cogadh Gaedhil re Gallaibh gives two accounts of the occupation: that Brian remained in Dublin from Christmas Day until Epiphany (6 January), or from Christmas Day until St. Brigid's Day (1 February). The later Annals of Ulster gives a date of 30 December for the Battle of Glenmama, while Annals of Inisfallen dates Brian's capture of the city two days later, to 1 January 1000. According the much more reliable Annals of the Four Masters and the Chronicon Scotorum, Dublin was only occupied for a week by Munster forces. In any case, in 1000 Brian plundered the city, burned the Norse fortress and expelled its ruler, King Sigtrygg Silkbeard.

According to the Cogadh Gaedhil re Gallaibh, Sigtrygg's flight from the city brought him north, first to the Ulaid and then to Áed of Cenél nEógain. Since Sigtrygg could find no refuge in Ireland, he eventually returned, submitted to Brian, gave hostages and was restored to Dublin. This was three months after Brian ended his occupation in February. In the meantime, Sigtrygg may have temporarily "turned pirate" and been responsible for a raid on St David's in Wales.

Brian gave his own daughter by his first wife in marriage to Sigtrygg. Brian in turn took as his second wife Sigtrygg's mother, the now thrice-married Gormflaith. The cessation of revolt was followed by over a decade of peace in Dublin while Sigtrygg's men served in the armies of Brian. However, Sigtrygg never forgot the insult of the Ulaid, and in 1002 he had his revenge when his soldiers served in Brian's campaign against the Ulaid and ravaged their lands.