Grianan of Aileach

Grianan of Aileach was constructed by the Northern Uí Néill in the sixth or seventh century CE atop Greenan Mountain in County Donegal. The circular stone fort, measuring approximately 23.5 metres in diameter with walls standing around 5 metres high, served as the royal capital and principal residence of the Cenél nEógain, a branch of the Northern Uí Néill and one of early medieval Ireland's mo...