The prevalence of fortified homesteads and small settlements in Ireland speaks of a violent and turbulent history. Much of the low-level conflict that went on was unrecorded; only major events found their way into mythology and survived long enough to be chronicled.

Dun Aengus (also Dun Angus and Dún Aonghasa) is located on Inis Mór, the largest of the three Aran Islands. The fort is precariously perched on the edge of a vertical cliff and consists of three irregular semicircles, each a line of defence and four defensive walls, which form semi-circular bulwarks. The original shape was presumably oval or D-shaped but parts of the cliff and fort have since collapsed into the sea. One mode of defence is a band of stones set in the ground that are closely packed, set at an angle and intended to thwart an attack up the slope. The cliff at the western edge of the fort is as sheer as the Cliffs of Moher, but at 100 m (300 ft) not as steep. It has been called ‘the most magnificent barbaric monument in Europe’.

Dún Aonghasa is believed to have been built and occupied originally in the Iron Age, although there was habitation at the site earlier, in the Bronze Age. The walls of Dún Aonghasa have been rebuilt to a height of 6m and have wall walks, chambers, and flights of stairs. The restoration is easily distinguished from the original construction by the use of mortar. There is a small museum illustrating the history of the fort and its possible functions. Also in the vicinity is a Neolithic tomb and a small heritage park featuring examples of a traditional thatched cottage and an illegal poteen distillery.

According to the Lebor Gabála (Book of Invasions), the mythological race of the Fir Bolgs (men of bags) settled in Ireland and once here, their leaders from the Fir Bolgs, the Failion and the Fir Domhnainn, divided Ireland into five provinces. These five ancient political divisions were referred to as cúigí (“fifths”) such as the fifth of Munster, the fifth of Ulster and so on. Later record-makers dubbed them provinces, in imitation of the Roman imperial provinciae. For some, the fifth province is an important province of the imagination, a province where all can meet. For the Fir Bolgs it was an administrative centre. Each province had a King who ruled over smaller Kingships. One was Eochy who married Tailtiu, in whose honour the Tailteann games were held to the mid Twentieth century.

The Fir Bolgs built Dún Aonghasa after they sought refuge on the island in the first century CE. They named the fort after their chieftain, Aenghus, King of the Clann Umoir, ‘the sterling pilot of his people who lives in legend as the founder and first lord of Dun Aengus.’

The Fir Bolgs possessed Ireland for thirty-seven years before being defeated by the Tuatha Dé Danann in the first Battle of Magh Tuireadh.

The writer J. M. Synge accepted this history as true history when he wrote about Dun Aengus, ‘I prop my book open with stones touched by the Fir Bolgs.’ Sir William Wilde, father of Oscar Wilde, hosted a reception in Dun Aengus in 1857 and in his remarks, he too accepted the Fir Bolgs as builders: ‘I believe I now point to the stronghold prepared as the last standing place of the Fir Bolg Aborigines of Ireland, to fight their last battle if driven to the western surge…’

Some Aran opinion, influenced by the 15th century Welsh historian Giraldus Cambrensis, accepts the Danes, Norse raiders of the ninth and tenth centuries, as the builders of Dún Aonghasa. Neither legend nor history helps to answer questions about Dún Aonghasa.

Lebor Gabála Érenn: The Book of Invasions of Ireland
§39-54: ‘The Nemedians and the Fir Bolg’