Domnall mac Taidc (died 1115) was the ruler of the Kingdom of the Isles, the Kingdom of Thomond, and perhaps the Kingdom of Dublin as well. His father was Tadc, son of Toirdelbach Ua Briain, King of Munster, which meant that Domnall was a member of the Meic Taidc, a branch of the Uí Briain. Domnall's mother was Mór, daughter of Echmarcach mac Ragnaill, King of Dublin and the Isles, which may have given Domnall a stake to the kingship of the Isles.

In 1094, Domnall's uncle, Muirchertach Ua Briain, High King of Ireland, drove Gofraid Crobán, King of Dublin and the Isles from Dublin, and may have replaced him with Domnall himself. Certainly at some point following Gofraid's death in 1095, Muirchertach installed Domnall as King of the Isles. The latter's reign was short-lived however, and Domnall appears to have been forced from the Isles prior to its subsequent conquest by the King of Norway.

In 1111, Domnall evidently seized the kingship of the Isles by force. It is uncertain whether he enjoyed Uí Briain support in this venture. Several years later, at a time when his aforesaid uncle was gravely ill, Domnall was again active in Ireland. Although he may have openly left the Isles to take advantage of his uncle's demise, it is also possible he was forced out by the Islesmen. Domnall was slain in 1115, apparently at the hands of Toirdelbach Ua Conchobair, King of Connacht.

Familial origins

Domnall was a son of Tadc, son of Toirdelbach Ua Briain, King of Munster.Ní Mhaonaigh (2018) p. 146 n. 83; Casey (2013) p. 147 fig. 2; Candon (2006) pp. 116, 117 fig. 4; Byrne (2001) p. 297 tab. 17; Duffy (1993a) p. 30; Duffy (1992) pp. 104–105, 105 n. 59; Kelleher (1988) p. 26 tab. Domnall was, therefore, a member of the Meic Taidc.Forte; Oram; Pedersen (2005) p. 445; Oram (2000) p. 20; Duffy (1992) p. 105. According to the twelfth-century Banshenchas, Domnall's father married Mór, daughter of Echmarcach mac Ragnaill, King of Dublin and the Isles. This source specifies that the couple had three sons and a daughter: Amlaíb, Bé Binn, Donnchad, and Domnall himself.Downham (2017) p. 100 n. 62; Downham (2013) p. 147; Duffy (2002) p. 55, 55 n. 7; Duffy (1993a) p. 34, 34 n. 16; Duffy (1992) p. 105, 105 n. 59; Candon (1988) p. 403; Dobbs (1931) pp. 196, 229.

Uí Briain intervention in Dublin

Toirdelbach Ua Briain died in 1086, and the Kingdom of Munster was partitioned between his three surviving sons: Muirchertach, Diarmait, and Tadc. The latter expired only a month after his father, after which Muirchertach drove Diarmait from Munster altogether, seizing the kingship for himself. Muirchertach then embarked upon extending his authority throughout Ireland.Duffy (2005). During this period, Muirchertach not only had to contend with the opposing forces of his surviving brother,Duffy (2005); Duffy (1992) pp. 104–105. but also those of the Meic Taidc, the sons of his deceased brother. In 1091, however, the Meic Taidc appear to have come to terms with Muirchertach—at least temporarily—as the seventeenth-century Annals of the Four Masters reports that a peace was agreed between him and the Meic Taidc, who are nonetheless said to have acted treacherously towards Muirchertach's men.Annals of the Four Masters (2013a) § 1091.10; Annals of the Four Masters (2013b) § 1091.10; Duffy (1993a) p. 34; Duffy (1992) p. 105, 105 n. 58; Candon (1988) p. 404. Although Muirchertach appears to have regained control of the Kingdom of Dublin by 1090, he soon after lost it to Gofraid Crobán, King of the Isles, until he forced the latter from the kingship of Dublin once and for all in 1094.Duffy (1992) pp. 106–108. It may have been at this point that Muirchertach installed his son, Domnall Gerrlámhach, to the kingship.MacCotter (2017); Flanagan (2008) p. 907. Another possibility, however, is that Muirchertach instead appointed Domnall himself after Gofraid's expulsion.Bracken (2004a).

Meic Taidc interference in the Isles

Gofraid died in the Hebrides the year after his expulsion from Dublin.Ní Mhaonaigh (2018) p. 146; Duffy (2006a) p. 63; Duffy (2004b). Whether this is evidence that he had been driven from Mann is uncertain.Forte; Oram; Pedersen (2005) p. 235; Oram (2000) p. 20; Duffy (1993a) pp. 35–36; Duffy (1993b) p. 16. According to the thirteenth- to fourteenth-century Chronicle of Mann, Gofraid was succeeded in the Isles by his eldest son, Lagmann,McDonald (2019) p. 23; Oram (2011) p. 48; Oram (2000) pp. 20–21; Candon (1988) p. 404; Power (1986) p. 116; Anderson (1922) p. 98; Munch; Goss (1874) pp. 54–55. who appears to have been forced to fend off factions supporting the claims of his younger brothers.Oram (2011) p. 48; Duffy (2004b); Oram (2000) p. 21. At some point, the chronicle claims that the leading Islesmen sought assistance of Muirchertach, and petitioned him to provide a regent from his own kin to govern the kingdom until Lagmann's younger brother, Amlaíb mac Gofraid, was old enough to assume control.Ní Mhaonaigh (2018) p. 146, 146 n. 83; Oram (2011) p. 48; Duffy (2009) p. 296; Candon (2006) p. 116; Duffy (2006a) pp. 62–63; Forte; Oram; Pedersen (2005) pp. 235–236; Power (2005) pp. 11–12; Bracken (2004a); Duffy (2002) p. 57; Holland (2000) pp. 128, 128–129 n. 79; Oram (2000) p. 21; Duffy (1997) p. 43; Ní Mhaonaigh (1995) p. 375; Ó Cuív (1994) p. 116; Duffy (1993a) p. 36; Duffy (1993b) p. 16; Duffy (1992) pp. 108–110; Power (1986) p. 115; Anderson (1922) p. 100; Munch; Goss (1874) pp. 54–55. The chronicle's account could be evidence that, by about 1096, Lagmann faced a faction formed around his younger brother; and that, when this faction was unable to topple Lagmann by itself, it approached Muirchertach for assistance in placing Amlaíb mac Gofraid upon the throne.Oram (2011) p. 48; Forte; Oram; Pedersen (2005) pp. 235–236; Oram (2000) p. 21. Muirchertach was certainly a formidable potential ally, having recently imposed his dominance over the kingdoms of Connacht, Leinster, Mide, and Dublin.Oram (2011) p. 48; Flanagan (2008) p. 909; Forte; Oram; Pedersen (2005) p. 235; Bracken (2004). In consequence of this predominance, the clause as stated by the chronicle—that Muirchertach was to provide the Isles with a regent from his own kin—may well have been a condition on his intervention, rather than a request of the Islesmen themselves.Forte; Oram; Pedersen (2005) pp. 235–236; Oram (2000) p. 21; Anderson (1922) pp. 100–101; Munch; Goss (1874) pp. 54–55. Whatever the case, the chronicle reveals that Muirchertach then installed Domnall upon the throne.Ní Mhaonaigh (2018) p. 146, 146 n. 83; Oram (2011) p. 48; Duffy (2009) p. 296; Forte; Oram; Pedersen (2005) p. 236; Power (2005) pp. 11–12; Bracken (2004a); Duffy (2002) p. 57, 57 n. 11; Oram (2000) p. 21; Duffy (1997) p. 43; Duffy (1993a) p. 36, 36 n. 25; Duffy (1992) pp. 108–110; Anderson (1922) pp. 100–101; Munch; Goss (1874) pp. 54–55.

Although Domnall had earlier opposed Muirchertach over the kingship of Munster, he possessed strong familial connections with the Isles through his maternal descent from Echmarcach.Forte; Oram; Pedersen (2005) p. 236; Duffy (1992) p. 109. In fact, the fifteenth- to sixteenth-century Annals of Ulster reveals that at least two apparent members of Echmarcach's family were killed less than a decade before in a repulsed invasion of Mann.The Annals of Ulster (2012) § 1087.7; Oram (2011) p. 32; The Annals of Ulster (2008) § 1087.7; Duffy (2006a) p. 62; Forte; Oram; Pedersen (2005) pp. 233, 236; Duffy (2002) p. 55; Oram (2000) pp. 19–20; Duffy (1993a) p. 34; Duffy (1992) pp. 105, 109; Candon (1988) pp. 403–404. As a result of their demise, Domnall may well have become the leading male representative of his mother's family.Forte; Oram; Pedersen (2005) p. 236; Oram (2000) p. 21; Duffy (1992) p. 109. From the standpoint of the Uí Briain, the union of Domnall's parents would, therefore, seem to have been orchestrated in the context of extending Uí Briain authority into the Isles.Candon (2006) p. 116; Candon (1988) p. 404. In 1096, the Annals of the Four Masters reveals that Domnall's brother, Amlaíb, lost his life on Mann,Annals of the Four Masters (2013a) § 1096.8; Annals of the Four Masters (2013b) § 1096.8; Ó Corráin (2010) p. 225; Candon (2006) p. 116; Duffy (2006a) p. 64; Forte; Oram; Pedersen (2005) p. 236; Power (2005) pp. 11–12; Duffy (2002) pp. 55, 57; Duffy (1997) p. 43; Duffy (1993a) pp. 34, 36; Duffy (1992) p. 109; Candon (1988) p. 404; Anderson (1922) p. 99. apparently whilst supporting Domnall's undertaking in the Isles.Duffy (2006a) p. 64; Duffy (2002) p. 57; Duffy (1993a) p. 36. This source not only corroborates Uí Briain intervention in the Isles,Duffy (2002) p. 57; Duffy (1993b) p. 16. but suggests that Domnall and the rest of the Meic Taidc faced significant opposition there,Candon (2006) p. 116; Forte; Oram; Pedersen (2005) p. 236. possibly in the form of Lagmann's adherents.Forte; Oram; Pedersen (2005) p. 236. The chronicle credits Domnall with an oppressive three-year reign that ended when the leading Islesmen revolted against him, and drove him from the kingdom back to Ireland.Ní Mhaonaigh (2018) p. 146, 146 n. 84; Candon (2006) p. 116; Duffy (2006a) p. 62; Forte; Oram; Pedersen (2005) p. 236; Power (2005) pp. 11–12; Candon (1988) p. 404; Power (1986) p. 115; Anderson (1922) p. 101; Munch; Goss (1874) pp. 54–55.

Norwegian ascendancy in Dublin and the Isles

The extent of Domnall's rule in the kingdom is unknown, and it is questionable whether he had any real authority in the northern Hebrides, furthest from Mann.Forte; Oram; Pedersen (2005) p. 236; Oram (2000) p. 21. In about 1097, Magnús Óláfsson, King of Norway sent a delegate named Ingimundr into the Isles to take possession of the kingdom. After installing himself on Lewis, Ingimundr was overthrown and killed whilst attempting to usurp the kingship.Forte; Oram; Pedersen (2005) p. 236; Oram (2000) p. 21; Power (1986) pp. 115–116. Ingimundr's rationale for seating himself upon an island on the edge of the kingdom may have been due to the fact that he was unable to gain any authority on Mann itself.Power (1986) p. 116. In fact, the chronicle reveals that civil war erupted there the following year,Forte; Oram; Pedersen (2005) p. 236; Oram (2000) p. 21; Power (1986) pp. 118–119; Anderson (1922) pp. 101–102; Munch; Goss (1874) pp. 56–57. and the chronicler Orderic Vitalis indicates that Mann was devastated to point of being a virtual desert by the time Magnús appeared on the scene.Power (2005) p. 13; Power (1986) p. 119; Forester (1854) p. 217; Le Prevost (1852) p. 29. The warring itself may have been related to the aforesaid factional struggles between Gofraid's sons.Forte; Oram; Pedersen (2005) p. 236; Oram (2000) p. 21; Power (1986) pp. 118–119. Although it is possible that it was Magnús who actually forced Domnall from the Isles,Candon (2006) p. 116. the fact the chronicle makes no mention of Domnall during the recorded conflict on Mann may be evidence that he had lost control of the island by then.