They campaigned together, defeating and mortally wounding Eogan King of Connaught in 558 on the River Sligo; defeating Ailill King of Connaught, wht tried to escape battle in his war chariot in 549 against their kinsman, Diarmaid King of Ireland and head of the southern Ui Neill, because Diarmaid had offended their cousin, St Columba. They also defeated the Irish picts in 562 and the Leinstermen in 563 both died of plague in 566, Domnall left three sons. 1 Eochaid ( K of Ireland 569 to 572, ruled jointly with his Uncle, Baetan, and was killed with him in 572 by Cronan ( K of Keenagh and Cianachta of Glengiven ) from him descened the later sept whose chiefs were styled O'Donnghaile ( ODonnelly) and who held Ballydonnelly in Co Tyrone. All these chiefs were famous soldiers and were hereditary marshals of O'Neill's military forces untilthe 17th century. 2 Colgu ( K of Ailech 572 to 580 ) was defeated and killed in 580 by his kinsman Aedh MacAinmire ( K of Tír Conal ) in rivalry for the over-kingship of the north 3 Aedh Uairdhnach ( K of Ireland 604 to 612, was a friend and benefactor of his cousin, St Mura, and defeated the Leinstermen and exacted the famous cattle tribute ( the borama ) which the Leinstermen never paid without a fight.
He died 612 at the ford of the two Graves in Louth, He had one son. Maelfithig ( K of Ailech 628 to 630 ) called by the chroniclers Chief of the Cinel Mac Earca, succeeded his cousin Suibhne Menn, as ruler of Ailech, but was killed in battle by Suibhne's brother Ernaine ( Chief of the Cinel Fearadhaigh ) who then took the kingship of Ailech in 630. Maelfithig had a son. Maelduin ( K of Ailech 671 to 681 ) who succeeded his kinsman Fergus ( grandson of Suibhne Menn ) in 671. He killed Dunchad 9 K of Oriel ) in 677 and burned Dun-Ceithirn and with it Dunghal ( K of the Irish picts ) and also Cenndaeladh ( K of Keenaght ) He was himself killed in battle in 681 at Leathairbhe, in rivalry against his kinsman Congal ( K of Tír Conal and afterwards K. of Ireland ) for kingship of the north. Maelduin married Cacht, daughter of Maelcobha ( K of Tír Conal ) and by her had a son. Fergal ( K of Ireland 710 to 722 Defeated the southern Ui Neill of Meath in 710 at Armagh and banished his eldest heir to Britain for committing a homicide at the annual festival assembly at Taltiu ( the fair at Teltown ) 1 August 716 . He exacted the cattle tribute from Leinster in 721 and was killed in battle in 722, leading 21,000 men against the Leinstermen at Allen, Kildare, he married secretly a daughter of Congal ( K. of Ireland ) who had killed his father, and by her had a son Aedh Alainn ( the handsome ) K of Ireland. Fergal married again, Athiocht daughter of Clan ( K of Keenaght ) and by her had two other sons, Niall Frasach ( of the showers ) King of Ireland, and Conchobhar, whose descendants were styled Ocaithain ( O' Cahan-O'Cane ); they seized Glengiven ( Dungiven in Co Derry ), conquered from the Clanachta or Keenagh, in the 12th century and thereafter produced the most powerful "ur-ri" ( under-kings ) among the Cinel Eoghain, with the duty of inaugurating the O'Neill himself as King of Tyrone. Niall Frasach " of the showers " ( K of Ireland 763 to 770 ) saw his reign open with three months of snow and continue with famine, earthquakes, and pestilence. Taking this as a bad sign, he abdicated in 770 and retired to Iona as a monk, where he died in 778. He married Eithne daughter of Breasal of Brega, and by her had a son Aedh Oirdnidhe" The Dignified" ( K. of Ireland 797 to 819 ) devastated Meath in 798 and Leinster also taking hostages from its King in 804. He punished the Ulaid in 805 for profaning St Patricks shrine, drove the Con naught invaders out of Meath in 805" as if they were goats and sheep," and sent ambassadors to Charlemagne. He was prevented from celebrating the fair Taltiu in 811 by the monks of Tallaght, whose territory had been violated, but made ample reparations. He defeated the Cinel Conal in 815 and died 819. He married Maedhbh, daugher of Inreachtach ( chief of Durias, in Antrim ) and by her had by other issue two sons: Niall Caille ( K. of Ireland ) Maelduin ( K. of Ailech ) Niall Caille ( K. of Ireland 833 to 846 ) deposed his cousin Murchad in 823 and became King of the North. In 827 he defeated the men of Oriel who had opposed the election of his personal confessor as Archbishop of Armagh. He routed the Norse invaders who landed at Lough Foyle in 823, and defeated the Danes twice more in 835, and again in 843. He defeated Feidhimidh ( K of Munster ) in 840, and defeated the Danes again in 846, but during the pursuit of the latter he was drowned in the flooded River Callain while trying to rescue one of his men. He married Gormfhlaith, daughter of Dunchad mac Domhnaill, by whom he had three sons and a daughter: Aedh Finnliath " White Hair " ( K. of Ireland Oengus, ancestor of the Cinel nOengusa. Flaithbertach, whose son, Ualghrg ( Royal Heir of the North ) who died 879, was ancestor of Aedh O'Ualghairg ( K. of Cinel Eoghain 1065 to 1067 ) . A daughter ( name unknown ) , who married Conaing ( K. of Brega ). Sha composed a poem on the battle of Cilluaindaighri, in which was slain her son, Flann. Aedh Finnliath " White Hair " ( K. of Ireland 862 to 879 ) went to war against the southern Ui Neill in 860 and invaded the camp of Maelsechlainn ( K. of Ireland ) but was driven back. He plundered all the Danish fortresses in Ulster and defeated the Danes near Lough Foyle in 866, after which " twelve score of their heads were counted before him. He won a great victory in 868 against heavy odds at Killaderry over the meath and Leinstermen, who were allied with the Dublin Vikings. The Bards called Aedh" Chief king of the Gael"; he died in 879, he was married to Maelmuire, daughter of Kenneth MacAlpin ( K. of the Scots ) by her he had two sons and a daughter: Domnall ( K. of Ireland ) Niall Glundubh " Black Knee " ( K. of Ireland ) A daughter ( name unknown ) who married Olaf "the young" ( Norse K. of Dublin 853 to 872 ) Olaf was killed in battle in 874 in Scotland.