8Long, Harry, and Etienne Rynne. "Dún Aonghasa." Journal of the Galway Archaeological and Historical Society 44 (1992): 11.
The authors on p. 17 suggest that Dun Aengus and its chevaux-de-frise play an important role in discussions of the origin of Celtic groups in Ireland. "The question of when and by what routes Celtic-speaking peoples first arrived in Ireland is fraught with controversy and doubt. The stone chevaux-de frise at Dún Aonghasa is seen as evidence of the influx from Iberia of people speaking Q-Celtic in the wake of the Roman conquest of 133 B.C.33. Some philologists, however, associate the Fir Bolg of Ireland with the Belgae of Belgium and France, who may have occupied sites where, earlier, wooded chevaux-de-frise have been found. Dún Aonghasa is thus at the centre of a debate in which the chevaux-de-frise is used to argue two different opinions."
One of the other three examples of chevaux-de-frise is also on the island of Inishmore, at Dun Dúbhchathair, the Black Fort. There is a virtual-reality view of this fort (from a distance) on the Dun Aengus page.