O'Neill [q. v.] and his wife Caitriona, daughter of Ardghal MacMahon, and was twentieth in descent from Niall (870?–919) [q. v.], king of Ireland. He was a young man in 1431, when he was taken prisoner by Neachtan O'Donnell, who released him as one of the conditions of a peace with Eoghan O'Neill. In 1435 Neachtan O'Donnell, in alliance with Brian óg O'Neill, decided to attack Eoghan O’Neill and his sons Enri and Eoghan óg. As soon as the news arrived, Eoghan, with Enri and his brother, marched into the heart of O'Donnell's country by the pass now known as the bridge of Duchary to the Rosses, the district between the Gweebara and Gweedore, co. Donegal, and there encamped. That a hostile army was able to live there shows that the district can hardly have been less productive then than it is now. O’Donnell attacked the O’Neills, drove them out, and occupied the camp. Enri O’Neill, after a short retreat, made a speech to his clansmen and to his gallowglasses, or hired men at arms, the MacDonnells, and again led them against the camp. He led the assault, and drove O`Donnell out. Mac Suibhne of Fanad, leader of the gallowglasses of O'Donnel1, 'obstinately resisted MacDonnell, and seems to have led off his men in good order. He retreated eastwards, probably with the intention of marching north along the Foyle, and so reaching Fanad, but was overtaken near Slieve Truiin, co. Tyrone, by Enri O’Neill. In the action which ensued MacSuibhne was defeated and taken prisoner. Brian O'Neill tried to get into favour by giving up O'Donnell’s castle of Ballyshannon, and coming to O'Neill with his two sons. O’Neill cut off one foot and one hand from each, and one of the sons died at once. In 1439 he marched to Fortora on Lough Erne. and released the chief of the Maguires, who had been made a prisoner in his own castle by one of his vassals. With some English allies he again defeated Neachtan O'Donne1l in 1442, and obtained from him Castle Finn, co. Donegal, the territory of Cinel Moain, and the tribute of Inishowen. In the same year he fought for MacQuillin against Aedh liuidh O’Neill, and in 1444 sustained a severe defeat fighting with MacQuillin against O'Neill of Claneboy, co. Down, and had to give up his son Aedh as a hostage. He again helped MacQuillin in 1450, and in the same year his son Niall was slain while on a foray by his cousin Enri, great-grandson of Enri aimhreidh. He aided his father in 1452 in obtaining an eric from Maehlahon, who had slain Macllonnell, the chief of O'Neill's gallowglasses. Enri O'Neill had married the daughter of MacMurchadha, a stepsister of the Earl of Ormonde, but had for some time been living with the daughter of MacWilliam Burke, widow of Neachtan O’Donnell. The Earl of Ormonde marched against him, and compelled him to send away Baintreabhach O’Donnell, and to take back his lawful wife. He deposed his father, who was probably in a state of senile decay. in 1455, and was inaugurated O’Neill at Tallahoge, in the presence of the Archbishop of Armagh and of all the O'Neills. He went to war with the O'Donnells in 1456, and established Toirdhealbhach Cairbrech as their chief, with whom in 1458 he successfully plundered Lower Connaught and Breifne. In 1459 he tried, with English allies, to take the castle of Omagh from the Sliocht Airt Ui Neill, but failed, and made peace with them. The king of England sent him forty-eight yards of scarlet cloth, a chain of gold, and other presents in 1463, thus recognising him a chief king of the Irish. In 1464 he plundered and burned Donegal as far as Ballyshannon, and in 1467 ravaged Oireacht Ui Cathain or O’Cahan’s country, co. His alliance with MacQuillin still subsisted, and they invaded Clanebo in 1470, and captured the castle of Sgatliideirge on Sketrick Island in Strangford Lough. In 1471, after a siege of six months, he took the castle of Omagh, and later in the year plundered Tirbreasail, co. Donegal. Five years later he again attacked the O’Neills of Claneboy, and demolished their castle of Belfast. In 1479 and 1480 he plundered Donegal. These were his last expeditions, and in 1483 he had his son Con inaugurated chief of the Cinel Eoghain in his stead, and after six years of retirement died in 1489. The poet Brian ruadh Mac Conmidhe [q. v.], who also praised his enemy, Neachtan O’Donnell, praises him as chief king of the Irish in a poetical address of which there is a late copy in the British Museum (Edgerton MS. 111).
[Annala Rioghachta Eireann. ed. O’Donovan, vol. iv.; Annals of Loch Cé, cd. Hennessy. vol. ii.; Transactions of Iberno-Celtic Soc. (O'Reilly), Dublin, 1820; S. Il. O'Grady`s Cat. of Irish MSS. in British Museum]
O'NEILL, HENRY (1800–1880), Irish archæologist, born at Dundalk in 1900, issued two works which are held in high estimation by Irish antiquaries. The first of these, entitled ‘The Most Interesting of the sculptured Crosses of Ancient Ireland, drawn to scale and lithographed by H. O'Neill,’ an imperial folio, containing thirty-six fine tinted lithographs with descriptive letterpress and an essay on ancient Irish art, was published by the author, London, 1857. It was followed by ‘The Fine Arts and Civilisation of