The Grianán Ailigh, Ireland

Called also Grianan of Aileach. It's very old hillfort placed on the 244 meters high on Greenan Mountain in County Donegal, Ireland.

Grianan of Aileach (in Irish: "The Grianán Ailigh") is very old hillfort, which was placed on the Greenan Mountain, 244 meters high in County Donegal, Ireland. The main fort structure is made of stone and it has been built in the 6th or 7th century by the Northern Uí Néill. There is evidence that the Grianan of Aileach had been in use before that time.