Dun Aengus, the largest prehistoric stone fort of the Aran Islands, is one of Ireland’s most popular attractions. It is enclosed by three massive dry-stone walls made of blocks of limestone set vertically into the ground to deter attackers. The fort sits on a 300 ft cliff and offers the visitor spectacular views of the Atlantic Ocean. Excavations carried out in the 1990s indicated that the cliff tops had been inhabited from as early as c.1500 BC with the first walls and houses being built c. 1100 BC. An amazing network of defensive stones surrounds the whole structure.