Fiachra Cossalach (died 710) was a Dál nAraidi king of the Cruthin in Ulaid, a medieval over-kingdom in Ireland.
Fiachra Cossalach was a son of Dúngal Eilni mac Scandail (died 681) and hence a member of the Eilne branch of the family.
[3] Curiously, Fiachra is mentioned as one of the guarantors of the Cáin Adomnáin at the Synod of Birr in 697 as king of the Cruithin at a time when Áed Aired (died 698) was considered to be king.
Fiachra himself met his death in 710, slain among the Cruithin.
His son Flathróe mac Fiachrach (died 774)[1] was also king of Dál nAraidi.