Situated on a hilltop 800 feet above sea level, the Grianan of Aileach is a reconstructed stone fort that was originally built on an earthen rath (Co Donegal).
The origins of the Grianan of Aileach are dated back to 1700 B.C. It is linked to the Tuatha de Danann who invaded Ireland before the Celts and built stone forts on top of strategic hills. They worshipped Dagda (the Good God) and he too is associated with the origins of Aileach. It was he who ordered the building of a stone fort to act as a burial monument to his dead son.
The round fort has been rebuilt largely without mortar to remain close to the original building. The interior has three terraces and wooden structures were built against the terraces to provide accommodation. The stone fort or cashel was rebuilt in the 1870’s. It is the centrepiece of the site, 75 feet in internal diameter with walls measuring over 16 feet in height and approximately 13 feet in thickness. The dry stonewalls contain two passages within them as well as terraces along their interior which would have allowed access to their summit.
The remains of the three earthen banks, which surround the cashel, are still visible in places. They are heather covered with possible ditches located in between. In the east northeast a gap in the banks indicates the location of an ancient road, which passed through them. The tumulus, located midway between the inner and middle bank in the southeast, is no longer visible due to the covering of heather. The well is located to the south of the cashel between the outer and middle bank. It is thought that St. Patrick visited the site in the 5th Century and baptised the local chieftain, Eoghan (from whom Inis Eoghan gets its name), here.
Two theories are put forward as to its function, whether it was a defensive or a ceremonial site. It was the royal site of the Northern UÌ Neill between the 5th and 12th Centuries A.D. According to the Annals of the Four Masters,Murtagh O’Brien, King of Munster, destroyed it in 1101 A.D.