The son of Eogan the splendid was Olioll Ollum whose mother was Beara, the Spanish princess. This Olioll entered into alliance with Conn of the Hundred Battles, and married Conn's daughter, Saba. Olioll Ollum, with the support of his father-in-law Con Cead Cathach, contended for the sovereignty of Munster with Lughaidh MacCon, a prince of the race of Ith, who was supported by Nemeth, prince of the Ernans. The battle took place at Ceann Febradh. In this battle single combats took place. The eldest son of Olioll Ollum, by name Eogan, slew Dadar, the Druid. Nemeth was slain by Cairre Riada. By this victory Olioll became king of all Munster.
Olioll had many sons, most of whom were killed in battle, and he died about 232 AD. He divided Munster into three parts: Desmond, South Munster, he gave to the eldest branch, who were called Eoganachts or Eugenians, after Eogan, the eldest son. Desmond comprised the Counties of Cork and Kerry, and part of Tipperary about Cashel. The ruling family of Milesian Desmond was the MacCarthy. To Cormac Cas was given Thomond or North Munster, which comprised Limerick and part of Tipperary, and afterwards, the County Clare was acquired by conquest by Lughaidh Meann, King of Munster, for the Dalcassians. The leading family in Thomond was the O'Brien. Olioll prescribed that Munster should be ruled alternately by the kings of Desmond and Thomond, but this rule was not always observed.
The third division of Munster, Ormond, in the east, was given to Kian, the third son, from whom are descended the Clan Kian, whose ruling family was that of the O'Carrolls, princes of Ely. The possessions of Kian consisted of eight tuatha, or baronies, all situated in ancient Munster. The chief residences of the O'Carrolls were Birr and Leap Castle. It is from the Kian that the O'Carrolls of Ely are descended.294