A castle stood on this island from the 12th century: in 1184, the Annals of Loch Cé report that a lightning bolt caused a fire: The Rock of Loch-Cé was burned by lightning, i.e. the very magnificent, kingly residence of the descendents of Máel Ruanaid where neither goods nor people of all that were there found protection; where six score, or seven score, of distinguished persons were destroyed, along with fifteen men of the race of kings and chieftains, with the wife of Mac Diarmada, i.e. the daughter of Ó hEidhin, and his son's wife, i.e. the daughter of Domhnall O'Conchobhair, and the daughter of Ó Dubhda, and the son of DonnchadhO'Maelbhrenuinn, and the son of Donn O'Mannachain,and the two daughters of O'Mannachain, and Mac Maenaigh, chieftain of Cenél-Builg, and the priest O'Maelbealtaine, and Gillachiarain Ó Connachtain, (i.e. a son of chastity and lamp of piety), and a countless destruction besides of good men; and every one of them who was not burned was drowned in this tumultuous consternation,in the entrance of the place; so that there escaped not alive therefrom but Conchobar mac Diarmata with a very small number of the multitude of his people.

[5]A rebuilt castle featured in the final part of the 1235 conquest of Connacht by Richard Mór de Burgh, 1st Baron of Connaught.

[6] By the early 19th century the castle was in ruin, until architect John Nash was commissioned to redevelop the structure as a summer house or folly.

Medieval buildings dating to the thirteenth century were excavated on the northern side of the island above the earlier fortification, but were not found to be connected to the standing enclosure wall.

High-status Gaelic artifacts were discovered, including silver pins, a gaming piece, and large collections of butchered cattle, boar, and sheep.

The enclosure wall was modified on the northern end of the island in order to provide a view from the main window inserted into the tower.