The Eoganachta emerged at the beginning of recorded history to become the dominant dynasty in the south of Ireland, the ancient kingdom of Munster, at approximately the same time as the U Neill in the north of the country. The name Eoganachta may indicate descent from a divine or human ancestor connected with the yew tree, suggesting a parallel with the Gaulish tribe, the Eburones, "yew people." The yew tree is said to have been regarded as sacred by the Eoganacht. The importance of this tree held right into the historic period, the ending of Eoganacht power is said to have been symbolized by the destruction of an ancient yew tree at the Eoganacht monastery of Emly by the Dal Cais. The genealogies claim that they descended from the mythical Eogan Mor (also known as Mug Nuadat), son of Ailill Olum. It may have been that the Eoganachta were colonists who returned or were driven from their conquests in Britain, which could account for the Latin borrowing for the name of their capital, Caisel (modern Cashel, County Tipperary, from castellum). Around the beginning of the fifth century, the rulers of some Irish kingdoms in North Wales were expelled by the original inhabitants, which may or may not be coincidental, although traditionally Munster colonists in Britain were said to have been the U Liathain and the Waterford Deisi. The favored-ally status of the Deisi with the Eoganachta in historical times may well stem from such colonial activities.
A remarkable feature of the Eoganacht kingship was its association with Caisel and Christianity. Unlike the capitals of the other provinces such as Tara, Emain Macha, or Cruachain, Caisel had not been a ritual center in prehistoric times and was associated in historic times only with the Eoganachta. Tfrechan’s seventh-century biography of Patrick tells us that Patrick himself baptized the sons of Nadfrafch super Petram Cothrigi at Caisel. This is an obvious invention but would appear to be an early effort to tie Munster in with Armagh and the supremacy of the U Neill. The story of Conall Corc and his sons and their acquisition of the kingship of Munster has some parallels with the tales that attach to Niall No^giallach and his rise to power in the north of Ireland. The legends of Corc of Caisel included both pagan elements, found in a seventh-century text, Conall Core and the Corcu Lofgde, and Christian elements, in the eighth-century texts, The Exile of Conall Core and The Finding of Caisel. The literati of the Eoganachta liked to depict the kingship of Munster as a benevolent place, more peaceful than the U Neill kingship in the north.
Six main branches may be identified: Eoganacht Aine, Eoganacht Chaisil, Eoganacht Glendamnach, Eoganacht Airthir Chliach, Eoganacht Locha Lein, and Eoganacht Raithlind. Others such as Eoganacht Arran; Eoganacht Ruis Argait, also called Ninussa; and the U Fidgenti in Limerick and U Liathain in Cork, who are included in the tract The Expulsion of the Deisi as one of the Eoganachta dynasties, may have been segments of the main branches or grafted onto the ruling stem at a later date in the case of the last two named. Ultimately all of the Eoganachta were said to have been descended from Eogan Mor, son of Ailill Olum. However, Eoganacht Raithlind (U Eachach Muman) and Eoganacht Locha Lein may also have been later grafts onto the main Eoganacht stock and rarely figured in the kingship of Caisel, which remained with a few exceptions in the grasp of the eastern Eoganachta, the descendants of Oengus mac Nad Frafch maic Cuirc of Caisel, who consisted of Eoganacht Chaisil, Eoganacht Glendamnach, and Eoganacht Airthir Chliach. Eoganacht Caisel were settled around Caisel itself; Eoganacht Glendamnach around Glanworth in north Cork; Eoganacht Aine at Knockaney in County Limerick; Eoganacht Locha Lein around Loch Lein in Killarney; and Eoganacht Raithlind in the Lee and Bride valleys to the west of Cork Harbor.
The Eoganachta had a complicated relationship with their vassal kingdoms. There seems no doubt that the Deisi of Waterford and the Muscraige (in at least six widely separated tuatha from north Tipperary to west Cork) acted as facilitators for the Eoganachta and were treated as favored allies, and extant texts show that the kingship of Caisel/Munster was based on mutual obligations between the king and his subkings and vassals. While the text may be aspirational rather than the letter of the law, it shows that the king of Caisel was expected to give compensatory gifts in order of precedence in return for the services, such as hosting, tribute, and so forth that he got from his vassal states.
The most notable kings of Munster were Cathal mac Finguine of Eoganacht Glendamnach (d. 742) and Fedelmid mac Crimthainn (d. 847), both of whom were notable warriors who went on the offensive against the ever-increasing power of the U Neill kings of Tara. The Eoganacht ruled Munster for over 500 years until the rise of the Dal Cais in the tenth century, who legitimated Brian Boru’s usurpation of the kingship of Munster in 978 by grafting an ancestor of their own, Cormac Cas, onto the Eoganacht genealogy as a son of Ailill Olum, brother of the eponymous ancestor of the Eoganachta, Eogan Mor. The Dal Cais version alleged that the Eoganacht had ignored a decree of Ailill Olum to have the kingdom alternate between the descendants of his two sons. Needless to say, this theory of alternation only lasted in Brian’s lifetime, as the Dal Cais had no intention of alternating with a weakened Eoganachta. The Eoganachta staged a comeback in the first quarter of the twelfth century in the person of Cormac Mac Carthaig and went on, even after the Anglo-Norman Invasion, to rule parts of Cork and Kerry until the fall of the Gaelic Order in the seventeenth century. The MacCarthys, O’Sullivans, O’Donoghues, O’Keeffes, Kirbys, Moriartys, and many other well-known Munster families claim descent from these rulers of early medieval Munster.
