Show Summary Details

Page of
PRINTED FROM Oxford Dictionary of National Biography. © Oxford University Press, 2018. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single article in Oxford Dictionary of National Biography for personal use (for details see Privacy Policy).

Mac Briain, Donnchad [Donough O'Brien]locked

(d. 1064)
  • Damian Bracken

Mac Briain, Donnchad [Donough O'Brien] (d. 1064), king of Munster, was the son of Brian Bóruma (d. 1014) and of Gormlaith (d. 1030), the sister of Máel Mórda Ua Fáeláin, king of Leinster, and former wife of Olaf (Amlaíb), king of the Dublin vikings. The battle of Clontarf in 1014 greatly weakened Brian's descendants, the Uí Briain of Dál Cais in north Munster. This was a time of intense competition among the provincial Irish kings and Mac Briain had great difficulty in retaining power over Munster. He had little prospect of continuing his father's attempts to extend control over much of Ireland and faced internal opposition. His half-brother Tadc was an equal claimant to the kingship and several Munster dynasties began to assert themselves at this time. In 1023 Donnchad had Tadc assassinated and at this point he began to show his power. In 1025 he marched north into Connacht, plundered the capital Cruachu, and returned with hostages. The following year he began to extend his influence to the east, taking hostages from Meath, Brega, Norse Dublin, and Leinster, and returned with the king of Osraige to Kincora, an Uí Briain stronghold. A significant recognition of his authority is recorded in this year when Abbot Amalgaid of Armagh and his 'venerable clerics' (annals of Inisfallen, s.a. 1026) spent Easter at Kincora.

Events in east Munster and Leinster cut short Donnchad Mac Briain's advance. Toward the end of the decade the kingdom of Osraige reached the zenith of its power under Donnchad Mac Gilla Pádraig. The ruling Leinster dynasty of Uí Dúnlainge lost out to the rising Uí Chennselaig led by the dynamic Diarmait mac Máel na mBó, whose wife was Derbforgaill (d. 1080), Donnchad Mac Briain's daughter. Both Mac Gilla Pádraig and Diarmait—frequently acting together—resisted the ambitions of the king of Munster. From this point, Mac Briain's influence was contained to the north-west by the powerful Áed Ua Conchobair, king of Connacht, and balanced by Diarmait mac Máel na mBó in Leinster to the south-east. However, it was the emergence of Toirdelbach Ua Briain, the son of his assassinated brother, that brought about the powerful combination of these two forces and Mac Briain's downfall.

In 1051 Áed Ua Conchobair invaded Munster and Donnchad Mac Briain's son Domnall Bán died in the encounter. Although Áed and Diarmait mac Máel na mBó were Donnchad's natural enemies, it is likely that their concerted attacks on Munster about 1054 were the result of Toirdelbach Ua Briain's intrigues. In that year Áed, with the support of Toirdelbach, attacked north Munster while Diarmait and the men of Osraige attacked from the east. In 1058 Toirdelbach, with the backing of Diarmait, again marched against his uncle. Donnchad had no choice but to flee before their advance, preferring to burn the city of Limerick rather than see it fall into their hands. When he did engage his enemies shortly after, at the battle of Slíab Crot, he suffered defeat. These events probably forced on Donnchad the realization of how destructive a joint assault could be. To outmanoeuvre Toirdelbach and escape such combined attacks in the future, Donnchad submitted to King Áed of Connacht in 1060. The tactic was unsuccessful, for in 1061 Áed destroyed Donnchad's fort of Kincora and burned the Dál Cais ecclesiastical centre of Killaloe. Diarmait of Leinster and Toirdelbach marched into Munster and secured the submission of the nobles of the plain of Munster. Donnchad's son, Murchad in Scéith Girr (‘Murchad of the Short Shield’), resisted Toirdelbach without success. When Diarmait departed, Toirdelbach was confronted by an army put in the field by Donnchad and his son. Again, Toirdelbach emerged victorious and was soon supported by the return of Diarmait. Mac Briain acknowledged defeat and left on pilgrimage for Rome, where he died in 1064. He is buried in the church of Santo Stefano Rotondo on the Caelian Hill, where a later plaque records him as king of Cashel and Thomond.

Although Donnchad Mac Briain's career has been seen as disappointing when compared to that of his father, Brian Bóruma, he did manage to secure his position as king of Munster and retained the kingship for four decades. In the early, dynamic, period of his career he attempted to continue his father's campaign to control Leinster and the east, a campaign that was realized in the reigns of his nephew Toirdelbach Ua Briain and great-nephew Muirchertach Ua Briain. An entry inserted in the annals of Inisfallen recording Mac Briain's marriage in 1032 to a daughter of Ragnall testifies to his interest in establishing dynastic links with the Norse. The genealogies in the Book of Lecan record that Donnchad had twelve sons, and elsewhere Gormlaith, daughter of Ua Donnocáin, king of Ára, is named as Murchad's mother. Donnchad's activity in proclaiming ecclesiastical ordinances and his convening of a Munster synod show a ruler intent on extending royal prerogatives and also point the way to the reforming practices of his Uí Briain successors, who made Munster the centre of church reform. The annals of Inisfallen record how Donnchad enacted a law in 1040 which attempted to enforce strict sabbatarianism. The annals of the four masters refer to a Munster synod held in 1050 at Killaloe under Donnchad's presidency 'where they enacted a law and a restraint upon every injustice, from small to great. God gave peace and favourable weather in consequence of this law' (AFM, s.a. 1050). Despite the exaggeration that can be expected from such sources, Donnchad Mac Briain's career was indeed largely peaceful. At a time when a ruler's success was measured by his ability to wage war, perhaps a different criterion should be applied to Donnchad and due recognition be given to his achievement in maintaining both peace and his grip on power.


  • S. Mac Airt, ed. and trans., The annals of Inisfallen (1951)
  • The Book of Lecan, ed. K. Mulchrone (1937)
  • W. M. Hennessy, ed. and trans., Chronicum Scotorum: a chronicle of Irish affairs, Rolls Series, 46 (1866)
  • W. M. Hennessy, ed. and trans., The annals of Loch Cé: a chronicle of Irish affairs from ad 1014 to ad 1590, 2 vols., Rolls Series, 54 (1871)
  • M. A. O'Brien, ed., Corpus genealogiarum Hiberniae (Dublin, 1962)
  • ‘The Dalcassians’, North Munster Antiquarian Journal, 3 (1942–3), 189–202
  • F. J. Byrne, Irish kings and high-kings (1973)
  • J. Hogan, ‘The Ua Briain kingship in Telach Óc’, Féilsgribhinn Eóin Mhic Néill, ed. J. Ryan [E. Ua Riain] (1940)
  • D. Ó Corráin, Ireland before the Normans (1972)
  • D. Ó Corráin, ‘The career of Diarmait mac Máel no mBó, king of Leinster’, Journal of Old Wexford Society, 3 (1970–71), 27–35
  • D. Ó Cróinín, Early medieval Ireland, 400–1200 (1995)
  • K. Hughes, The church in early Irish society (1966)
  • M. T. Flanagan, Irish society, Anglo-Norman settlers, Angevin kingship: interactions in Ireland in the late twelfth century (1989)
J. O'Donovan, ed. and trans., , 7 vols. (1848–51); 2nd edn (1856); 3rd edn (1990)
S. Mac Airt & G. Mac Niocaill, eds., (1983)