This small univallate fort stands on an inland cliff near the western end of Inis Mór. Limited archaeological excavations carried out here in 1995 suggest that the fort was built in the period 650 - 800AD. During this period, Arainn was renowned as a centre of ecclesiastical learning and attracted followers and pilgrims from far and wide. By patronising the early monasteries the wealthy inhabitants of Dún Eoghanachta no doubt reaped some economic benefit. In addition they may have exerised considerable control over the food supply and the provision of transport to and from the island.