Dún Aonghasa is the largest prehistoric hill fort on the Arans. It lies at the edge of an app. 100 m high cliff. Most of the structures in Dún Aonghasa date back from the Bronze Age and the Iron Age. This covers a time from round about 1100 B.C. (first constructions) to 500 B.C. (triple wall). It is speculated that the primary purpose of Dún Aonghasa was a ceremonial one. Parts of Dún Aonghasa have been reconstructed. In the reconstruction mortar has been used, while the original walls are dry stone constructions.