Dictionary of National Biography, 1885-1900/Tuathal
TUATHAL (d. 544), king of Ireland, called Maelgarbh, Roughcrown, to distinguish him from Tuathal Teachtmhar, to whom the Irish historians attribute the subjugation of the Aithech Tuatha and restoration of the Milesian line in a. d. 76, was son of Cormac the blind, son of Cairbre, son of Niall Naighiallach [q. v.], and was therefore second cousin of Muircheartach Mor [q. v.], whom he succeeded in 533 as king of Ireland. His power was resisted by the Cianachta, a tribe in the east of Meath and Louth, but he defeated them at the battle of Cluanailbhe in Meath. They had probably supported Dermot's claim to be ardrigh; Dermot was son of Cearbhall, son of Conall Cremthain, son of Niall Naighiallach, and, after the defeat of the Cianachta, he was obliged to live as a fugitive, and as such took part in the foundation of Clonmacnoise [see Ciaran]. According to a story in the English version of the ‘Annals of Clonmacnoise,’ Tuathal offered a reward for Dermot's heart. Dermot's foster brother Maelmordha rode into Tuathal's presence with an animal's heart on a spear, as if to claim the reward, and when close to the king stabbed him with the spear and was himself slain. This assassination is said to have taken place in 544 at a spot called Greallach, but which of the several localities called by this Irish equivalent of Slough is not clear in the chronicles. Dermot succeeded Tuathal as king of Ireland.
[O'Donovan's Annala Rioghachta Eireann, i. 181, Dublin, 1851; Hennessy's Annals of Ulster (Rolls Ser.), i. 48.]