Grianán Ailigh is in the Republic of Ireland, near the border with Northern Ireland. It is located in Inishowen in County Donegal. It is a hillfort made out of stone that dates to the sixth century at least and seems to have been abandoned around the twelfth century.
The hillfort is said to have been the cradle of the ruling dynasty of Ó Néill. In mythology and folklore, the ring fort was said to have been built by the Dagda around the grave of his son Aedh who was killed by a Connacht chieftain. The poem that talks about the building of the ringfort may be found in the Book of Lecan.
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