These fortifications, built on naturally defensible headlands jutting into the sea, were strategically positioned to take advantage of steep cliffs on three sides, requiring defensive walls only across the narrow neck connecting them to the mainland. While the exact date of this particular fort remains uncertain, similar sites across Ireland typically date from the Iron Age through to the early medieval period, roughly 500 BC to 1200 AD.

The fort at Castlequarter follows the classic promontory fort design, where ancient inhabitants modified the natural landscape to create a secure settlement or refuge. The builders would have constructed ramparts, ditches, or stone walls across the landward approach, whilst the sea cliffs provided natural protection on the remaining sides. These sites often served multiple purposes; as defensive strongholds during times of conflict, seasonal settlements for communities engaged in fishing or trade, and possibly as ceremonial or high-status locations given their commanding views and dramatic settings.