Dún Aonghasa

Dún Aonghasa is a prehistoric stone fort occupying a clifftop site on the southwest coast of Inis Mór, the largest of the Aran Islands, with half of its original circular structure lost to coastal erosion leaving an open semicircle directly above a 100-metre drop to the sea. The fort comprises three concentric stone walls, the outermost enclosing a field of close-set stone spikes known as a chevaux de frise. Its construction is tentatively dated to the Bronze Age with subsequent Iron Age modifications.