Huge stone fort perched on a cliff 200 feet above the sea on the south-west coast of Inishmore, the largest of the Aran Islands. The fort, often described as one of the most magnificent structures of its kind in Western Europe, covers about 11 acres and comprises three concentric semicircles. The middle wall is covered by an abatis (or chevaux-de-frise) of jagged limestone uprights. The innermost semicircle has wall-walks and wall-chambers and a massive entrance-passage. Extensive restoration work, begun by the Office of Public Works in 1881, was ill-advised and made no record of the found state of the stone fort until that time. According to the Lebor Gabála [Book of Invasions], the Fir Bolg built Dún Aonghusa and other stone forts on Aran Island; one of their chiefs, Angus (3) (Aonghus, etc.), gives his name to the structure. It is also the last refuge of the Fomorians. Curiously, Dún Aonghusa does not figure prominently in island folklore, although it is called Coillnamhan Fort in the fiction of island-born writer Liam O'Flaherty (1896–1984).