Ard Fothaidh derived its name from Fothadh, son of Conall (descended from Niall of the Nine Hostages). Said to have been the royal residence of several Ard Rí or High Kings of Ireland in the 6th and 7th centuries, namely Ainmire Mac Seadna (born .c. 515) his son Aodh Mac Ainmire, and his son Domhnall.

Patrick prepared to found a church in Ard Fothaidh, and had set up a stake to mark the spot but then prophesied that Domhnall, son of Aodh, son of Ainmire, would build his royal dún in that place, which afterwards came to pass.

The two outer defensive rings of the fort are still identifiable. It may be considered second only to Aileach in Co. Donegal.