The site, whose name likely derives from Eas Gephtine meaning “Gephten’s Cascade” after a nearby waterfall, was first fortified by the Anglo-Normans in 1199 when William de Burgo recognised the defensive potential of this easily defendable island. By 1300, Askeaton had grown into a prosperous incorporated settlement, contributing to Edward II’s Scottish military campaigns, before passing into the hands of the powerful Earls of Desmond in the mid-fourteenth century, who would hold it as one of their principal residences for the next two centuries.

The castle complex consists of two distinct wards built primarily from local limestone. The outer ward follows the lozenge-shaped outline of the island, measuring roughly 142 metres north to south and 82 metres east to west, whilst the inner ward occupies a raised limestone outcrop at its centre. The most remarkable survival is the great hall on the western perimeter, a rectangular structure that reveals two distinct building phases; its thirteenth-century core of roughly coursed rubble was substantially remodelled in the fifteenth century with dressed ashlar, when the ground floor was vaulted and the building heightened. This two-storey hall, measuring approximately 32 metres by 14 metres, originally featured four pairs of large windows in its central chamber, though most were replaced with defensive gun loops during the later alterations, reflecting the changing military requirements of the age.

The castle’s strategic importance made it a prime target during the Elizabethan conquest of Munster, surviving an attack in 1579 that saw the nearby Franciscan Friary burned, only to fall to Lord Justice Pelham the following year. Despite receiving a new charter in 1613 that established a corporation with a sovereign and twelve burgesses, and the right to return two members to parliament until 1800, Askeaton never developed beyond a small market town. The castle’s military significance ended when it was slighted by Parliamentary forces in 1652, and today its substantial ruins, including the impressive hall with its intact gables rising 14.5 metres high, offer visitors a remarkable window into the evolution of Anglo-Norman fortification in Ireland.