Goat Island, in Roaringwater Bay, holds this structure at its edge, where the land runs out into the sea and the water does the work that walls might otherwise do. Promontory forts, known in Irish as dúnta, make use of natural coastal geography by cutting off a headland or island tip with an earthen bank, a stone rampart, or a combination of both, leaving the sea cliffs on the remaining sides to serve as the defences. The result is an enclosure that requires relatively little construction to secure a naturally strong position.

These coastal forts are found all along the Irish shoreline and date broadly to the Iron Age and early medieval periods, though many are difficult to date precisely without excavation. Their purposes were likely varied, encompassing settlement, seasonal use, storage, and the control of coastal approaches. On a small island such as Goat Island, the site would have been particularly isolated, accessible only by water, which adds a further layer of natural protection beyond the rampart itself. The specific details of this fort, its dimensions, the character of its defences, and any finds or structural features associated with it, remain incompletely documented in the public record at present.