In the epochal battle of the forces of Ireland
against the Vikings and their Irish allies at Clontarf in 1015 the forces of South Munster
( Ui Echach) were commanded by Cian of Cineal Aodh (Hugh’s People.) Second in command was
Domhnal (Donald), chief of Cineal Laoghaire (Leary’s People), and son of a recent king of Munster, Dhuiv da Boirrean. After the battle, while the forces of Munster were on their way home, Domhnal made a move to replace
Donnchadh, son of Brian Borumnha, as king by
demanding the return of the Cineal Laoghaire hostages. However, he was obliged to withdraw his demand when Cian, who was married to a daughter of Brian, refused to support him.
The consequence was that Domhnal turned on the Cineal Aodh after more than 500 years of harmony and defeated them decisively in a battle at Magh Guildhe near Bandon in West
Cork . Next he took on the Dal gCas at Limerick, without support from other Eoghanachta tribes,
in an attempt to return the throne of Munster to the Eoghanachta. He was badly beaten and lost his life.
For the next 150 years his descendants, beginning with his son Donnchadha, from whom the O Donoghues derived their patronymic,
occupied themselves with moving their homeland from West Cork to Kerry.