The Battle of Clontarf in Icelandic literature

Approximately 170 years after the composition of the Cogadh Gaedhel re Gallaibh, the battle of Clontarf appears in another medieval text, an Icelandic literary work entitled Brennu Njál's Saga (hereafter referred to as Njál's Saga).  This work was written c.1250-1280. The author of this work is unknown, but scholars have definitively determined it was created in Iceland. The events described in Njál's Saga allegedly took place some 200-300 years before the composition of the text, the majority taking place between c.960-1020.

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The primary plot concerns the issues surrounding blood feud, venegance killing, and the honor code within medieval Iceland. The saga's two main protagonists, Njál and Gunnar, both meet grisly and untimely ends due to a neverending cycle of feud and vengeance primarily instigated and sustained by their wives. Gunnar is ultimately violently defeated by his enemies and Njál meets an equally disasterous fate.

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Did you know? The Old Norse title of Njál's SagaBrennu Njál, translates as 'The Story of Burnt Njál' because Njál and his family are burned to death in their home

Myth and History

Njál's Saga, like the Cogadh, is literary in nature but, like the former text, its narrative is concerned with events and people of known or believed historical veracity. Scholars have attempted and have sometimes been successful in confirming the reality of some of the events in the saga. For example, excavations concerning a site called Bergthorshvol, the alleged home of Njál and his family, show signs of being burnt down, and this confirms for some scholars the truth of Njál's Saga account of the family's demise. 

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The 'Clontarf Episode' in the Njál Saga

Brian Boru, Gormlaith, Sitric and others appear in this text in what scholars have called the 'Clontarf Episode'. The series of events is somewhat distinct from the account of the Cogadh.

For example, Sitric is the main opposing force to Brian Boru, as opposed to Máel Mórda.

Additionally, Gormlaith's portrayal is much more prominent and unquestionably negative. However, this is well in line with the other female characters of the saga who are primarily portrayed as instigators of violence in the feud between Njál and Gunnar. The role of female inciters is a common literary role of women in broader tradition of the Old Norse sagas.  In the account of Clontarf containing Njál's Saga, a Viking named Brođir was responsible for Brian's death.

Now Brodir saw that King Brian's men were chasing the fleers, and
that there were few men by the shieldburg.

Then he rushed out of the wood, and broke through the shieldburg,
and hewed at the king.

The lad Takt threw his arm in the way, and the stroke took it off
and the king's head too, but the king's blood came on the lad's
stump, and the stump was healed by it on the spot.

Then Brodir called out with a loud voice, "Now let man tell man
that Brodir felled Brian."

George Webbe Dasent, Njál's Saga, p. 326-327.

Sources: 

Theodore M. Andersson, “The King of Iceland.” Speculum, Vol. 74, No. 4 (Oct. 01, 1999), pp 923-934.

Zoe Borovsky, 'Never in Public: Women and Performance in Old Norse Literature' in The Journal of American Folklore, Vol. 112, No. 443 (Jan 01, 1999), pp 6-39.

Alexander Bugge, 'The Origin and Credibility of the Icelandic Saga' in The American Historical Review, Vol. 14 No. 2 (Jan 01, 1909), pp 249-261.

Robert Cook, intro. and trans. Njal’s saga (London, 2001).

Lars Lönnroth, Njal’s saga: A Critical Introduction (Berkley, 1976).

Magnus Magnusson and Hermann Palsson, intro. and trans., Njal’s saga (Harmondstown, 1960).

William Ian Miller, Bloodtaking and Peacemaking: Feud, Law and Society in Saga Iceland (Chicago, 1990).

Harold Mytum, 'The Vikings and Ireland: Ethnicity, Identity, and Culture Change' In Contact, Continuity and Collapse: The Norse Colonization of the North Atlantic, edited by James H. Barrett (Turnhout, 2003), pp 113-37.

Donnchadh Ó Corráin, 'Viking Ireland: Afterthoughts' In Ireland and Scandinavia in the Early Viking Age, edited by Howard B Clarke, Máire Ní Mhaonaigh, and Ragnall O’Floinn (Dublin, 1998), pp 421-452. 

Brian Ó Cuív, 'Personal Names as an Indicator of Relations Between Native Irish and Settlers in Viking Period' in John Bradley (ed), Settlement and Society in Medieval Ireland: Studies presented to F.X. Martin, O.S.A. (Kilkenny, 1988), pp 79-88.

Trivia: 
According to Njál's Saga, Bróđir was executed by having his intestines cut out and wrapped around a tree until he died.