O'LOCHLAINN, DOMHNALL (1048–1121), king of Ireland, born in 1048, was son of Ardghal, chief of the Cinel Eoghain and lord of Oilech, who received the submission of Connaught in 1063, died at Tullaghoge, and was buried at Armagh in 1604. Domhnall became king of Oilech, as the chief of Cinel Eoghain was called, in 1083, and immediately made a foray into Conaille (co. Cavan), whence he carried off a large number of cattle. In 1084 he plundered Ulidia (Down and Antrim), and also attacked and slew Domhnall O'Gairmleaghaidh, a weak neighbour. In 1087 he slew another minor chief, Domhnall O'Laithen, and made an unsuccessful expedition into Meath. In 1088 he invaded Connaught, and received the submission of Ruadhri O'Conor [q.v.] , the king, marched on into Munster as far south as Kilmallock, co. Limerick, plundering Emly, co. Tipperary, Loch Gur, Bruree, Dunachip, Drummin, and Singland, co. Limerick, and Ceanncoradh, co. Clare, and bringing home eight score hostages, afterwards redeemed by Murtough O'Brien [q.v.] for a ransom of cows, horses, gold, and silver. He slew two of his kinsmen on one day in 1090, Maelruanaidh O'Cairellan of Tirkeeran, co. Londonderry, and Gillachrist O'Luinigh, chief of Cinel Moen, and in the same year received a formal submission from Muircheartach O'Brien, king of Cashel or Munster, Domhnall O'Maeleachlainn, king of Meath, and Ruadhri O'Conor, king of Connaught; and thenceforward the chroniclers speak of him as king of Ireland. The Danes of Dublin gave him two hostages to secure his passive support in a plundering expedition which they made into Magh Breagh as far as Athboy, co. Meath, with O'Brien. He captured Aedh O'Cannanain, chief of the Cinel Conaill (co. Donegal), in 1093, and put out his eyes, and thenceforward ruled the Cinel Conaill, and led them with him into all his wars. In 1094 he again invaded Ulidia, and slew Donnsleibhe O'Heochadha, its king, at the battle of the pass of Gortinure, co. Londonderry, after which he marched south at the head of the Cinel Eoghan and Cinel Conaill, and, in alliance with the Danes of Dublin under their king Godfrey, defeated the Munstermen and the men of Leinster and Ossory at Oughterard, co. Kildare. He then returned to Ulster, while the Munstermen marched east, drove Godfrey out of Dublin, and forced the king of Meath, who had also joined in the attack, to fly to the north. Four years later he repelled an invasion of Ulster by Muircheartach O'Brien at Fidh Conaille, co. Louth. The archbishop of Armagh made peace between them; but in 1099 a second attack was made by the Munstermen near Slieve Fuaid, co. Armagh, where Domhnall again held them in check. A year's peace between the north and south was then made by the archbishop. Domhnall crossed into Ulidia between Lough Neagh and Lough Beg, and after a battle at Creeve, co. Antrim, chiefly between horsemen, the Ulidians gave up an abbot and two chiefs as hostages. He cut down the great tree called Craobh Tulcha, under which the kings of Ulidia were inaugurated. As soon as the year of peace was up, Muircheartach O'Brien tried to invade Ulster at Assaroe, co. Donegal, but was driven back by Domhnall, who afterwards marched on into Meath and brought home much booty. O'Brien, with the aid of a Danish fleet, attacked Derry from the sea, and was again defeated; but in 1101 he got into Ulster at Assaroe, and destroyed Grianan Oiligh, near Londonderry, in revenge for the sack of Cenncoradh by Domhnall. Domhnall's son and his foster-brother had been captured by the Ulidians, and he gave up Donnchadh O'Heochadha, their king, whom he had captured some years before, in exchange. In 1102 Domhnall MacAmhalghaidh, archbishop of Armagh, took hostages from him and from O'Brien for another year's peace between them. In 1103 he expelled the successor of that O'Cannanain, whom he had blinded in 1090, and again made war on the Ulidians, who obtained aid from Munster, Leinster, Connaught, Ossory, and Meath. Domhnall held them in check near Armagh till O'Brien, with most of his men and the men of Meath and Connaught, marched away. He then fell upon the Leinstermen, who were supported by some Munstermen, the clans of Ossory, and some Danes of Dublin, and defeated them with great slaughter on 7 Aug. 1103, near Donaghmore in the barony of Iveagh, co. Down. Domhnall obtained much spoil. In 1106 he permitted Ceallach, archbishop of Armagh, to make a general visitation of Ulster, and to receive a cow from every six inhabitants. The archbishop again prevented a battle between Domhnall and O'Brien at Slieve Fuaid, co. Armagh, in 1109. He made peace in 1111 with his old enemy, Donnchadh O'Heochadha, king of Ulidia, in 1112 attacked the Danes in Fingall, co. Dublin, and carried off many cattle and prisoners; and in 1113 again made war on Donnchadh, drove him from Ulidia, and caused his own tribe to put out his eyes. Twice during this year, near Armagh and at Greenoge, co. Meath, the archbishop prevented a battle between O'Brien and O'Lochlainn. After marching to Rathkenny, co. Meath, in 1114, O'Lochlainn took hostages from the men of Meath, and, with the Connaughtmen,
