Fiachnae mac Áedo Róin

Fiachnae mac Áedo Róin (died 789) was a Dál Fiatach ruler of the over-kingdom of Ulaid in Ireland. He reigned from 750 to 789. He was the son of Áed Róin (died 735) and brother of Bressal mac Áedo Róin (died 750), previous kings. This family had their base in modern-day County Down, Northern Ireland.

His father had been slain in battle in 735 by the High King of Ireland Áed Allán (died 743) of the Cenél nEógain and the kingship of Ulaid passed to the rival Dál nAraidi of southern County Antrim in the person of Cathussach mac Ailello (died 749). However, in 749 Cathussach was killed at Ráith Beithech (Rathveagh, modern County Antrim) probably in the interest of the Dál Fiatach and Fiachnae's brother, Bressal, became king. Bressal himself was killed in 750 but the Dál Fiatach retained the kingship. The historian Professor Byrne, however, believes that it is probable there was an interregnum in Ulaid between the reigns of Áed Róin and Fiachnae.

Fiachnae restored the fortunes of the Dál Fiatach during his long reign. In 759 he became involved in a dispute among the churchmen of Armagh. Fiachnae supported the abbot Fer-dá-Chrích versus a priest named Airechtach who had the support of Dúngal mac Amalgado of the Uí Néill of Brega. Fiachnae defeated them at the Battle of Emain Macha, near Armagh, and Dúngal and his ally Donn Bó mac Con Brettan, king of Fir Rois were slain.

In 761 Fiachnae defeated the Uí Echach Cobo (a branch of the Dál nAraidi) of the west part of county Down in the Battle of Áth Duma where their king Ailill mac Feidlimid was slain. The Uí Echach Coba were to suffer another defeat in 776 this time at the hands of the Airthir (an Airgialla tribe of modern County Armagh).

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