Dún Aonghasa (anglicized Dun Aengus) is the most famous of several prehistoric forts on the Aran Islands of County Galway, Ireland. It lies on Inishmore, at the edge of a 100 metre high cliff.
It is not known when Dún Aonghasa was built, though it is now thought to date from the Iron Age.
Today we know that the first construction goes back to 1100 BC, when the first enclosure was erected by piling rubble against large upright stones. Around 500 BC, the triple wall defences were probably built along the western side of fort.
Built on a high cliff some one hundred metres above the sea, It may have been used for seasonal rites by the druids