The Grianan of Aileach, sometimes anglicised as Greenan Ely or Greenan Fort, is a hillfort atop the 244 metres high Greenan Mountain at Inishowen in County Donegal, Ireland.

What does grianan mean in Gaelic?

The word Grianán means sunny place. It was appropriated by the early Irish to mean a place with a view. This is probably the sense in which the word was used to describe the Grianán under discussion.

When was an Grianan Fort built?

The origins of the Grianán of Aileach fort are dated back to 1700 BC. 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.