A popular tourist attraction, Dún Aonghasa is an important archaeological site that also offers a spectacular view. It is not known when Dún Aonghasa was built, though it is now thought to date from the Iron Age. T. F. O'Rahilly surmised that it was built in the 2nd century BCE by the Builg following the Laginian conquest of Connacht. Today we know that the first construction goes back to 1100 BCE, when the first enclosure was erected by piling rubble against large upright stones. Around 500 BCE, the triple wall defences were probably built along the western side of fort.