The sons of Niall of the Nine Hostages, seven in all, were Conall Gulban, ancestor of the Cenél Conaill dynasty, Éndae, progenitor of the Cenél nÉndai, Eógan mac Néill, ancestor of the Cenél nEógain dynasty, Conall Cremthainne, ancestor of both the Clann Cholmáin and Síl nÁedo Sláine dynasties, Coirpre, ancestor of the Cenél Coirpri, Lóegaire, progenitor of the Cenél Lóegaire, and Fiachu, progenitor the Cenél Fiachach.
Together these dynasties are known to historians as the Uí Néill. They are then divided into the Northern Uí Néill, comprising the first three mentioned above, and the Southern Uí Néill, comprising the remainder. The Cenél nEógain established themselves in western Ulster with their capital at Ailech which centers around what is today known as Innishowen in County Donegal. The Kings of Ailech were often the Northern Uí Néill overkings, who for several centuries rotated as Kings of Tara with the Southern Uí Néill overkings. For most of that period the Tara kingship was rotated exclusively between the dominant Southern Uí Néill Clann Cholmáin and the Northern Uí Néill Cenél nEógain. The system finally broke down in the 10th century.
The O’Neill dynasty is a continuation of the Northern Uí Néill Cenél nEógain dynasty, descendants of the 5th century Eógan mac Néill, through the 10th century Niall Glúndub.
A son of Niall Glúndub was Muirchertach mac Néill, father of Domnall ua Néill, who was the first king to be named High King of Ireland in his obituary. Through Domnall’s grandson Flaithbertach Ua Néill descend the Kings of Tír Eógain, or Tyrone, and the O’Neill dynasty. Most closely related to the O’Neills are the Mac Lochlainns, also of the Cenél nEógain, who in addition to providing two High Kings, Domnall Ua Lochlainn and Muirchertach Mac Lochlainn, also contested the kingship of Tyrone with the O’Neills until the mid-13th century.
In the 12th century, the O’Neill’s began to challenge their cousins, the MacLoughlins. After more than a century of warfare between the two clans, the O’Neills along with to the O’Donnells defeated & nearly wiped out the MacLoughlins and went on to dominate central Ulster. Over time the greater O’Neill sphere of influence self divided into three major O’Neill lordships. Later, both the chief rivals and allies of the O’Neills in Ulster were the O’Donnell dynasty of Tyrconnell, a continuation of the Northern Uí Néill Cenél Conaill.
Tyrone was the traditional stronghold of the various O’Neill clans and families, the strongest of the Gaelic Irish families in Ulster, surviving into the seventeenth century. The ancient principality of Tír Eoghain, the inheritance of the O’Neills, included the whole of the present counties of Tyrone and Londonderry
The date of the construction of Tullyhogue fort is not known, however it is believed to have held great significance from early times, possessing a form of ritual importance long before the O’Neills became associated with the site.
Tullyhogue rath was originally associated with the Uí Tuirtre of Airgialla, and then with the O’Hagans between the 11th and 17th centuries. The O’Hagans dwelt at the site and became its hereditary guardians, with their burial place at Donaghrisk situated at the bottom of the hill. In the later medieval period it became the inauguration site of the O’Neill dynasty, where the title “the O’Neill”, was bestowed upon each new lord. The inauguration was carried out by the heads of the O’Cahan and O’Hagan. O’Cahan, the O’Neill’s principal sub-chief, would throw a golden sandal over the new lord’s head to signify good fortune. O’Hagan, being the hereditary guardian of Tullyhogue, would place the shoe on the O’Neill’s foot and present him with a rod of office.
Hugh O’Neill’s inauguration in 1593 was the last such event for an O’Neill to take place at Tullyhogue. The last coronation that is claimed to have taken place at Tullyhogue was that of Sir Phelim O’Neill in 1641, however it was later rejected.