Forggus mac Cellaig

Who was Forggus mac Cellaig?

Forggus mac Cellaig was a King of Connacht from the Uí Briúin branch of the Connachta. He was the son of Cellach mac Rogallaig, a previous king and brother of Domnall mac Cellaig. The sept of Uí Briúin Ai he belonged to was the Síl Cellaig of Loch Cime named for his father. He reigned from 742 to 756.

Events occurred in his reign which helped to weaken the other branches of the Connachta. In 743 a battle was fought between the Ui Fiachrach Aidhne and their ex-allies the Ui Maine. Also in 743 the Ui Aillelo fought a battle in Mag Luirg with the Gailenga.

Fergus himself had to impose his authority and in 746 in alliance with the Conmaicne he was defeated by opponents from the Uí Briúin. That same year he slaughtered The Uí Briúin Seóla branch in southern Connacht. In 752 the Ui Briun destroyed the Calraige Luirg, who were possibly vassals of the Ui Aillelo. In 753 the Ui Aillelo were slaughtered by the Grecraige.

The Ui Briun expansion to the north met with the hostility of the Cenél Coirpri branch of the Ui Neill. In 754 was fought the Battle of Ard Noíscan in Ui Aillelo territory between the Ui Briun and the Cenel Coipri. In 756 he inflicted a heavy defeat on them at the Battle of Móin Mór.