A promontory fort is exactly what it sounds like: a defensive enclosure built on a headland, where the sea does much of the work, dropping away on three sides and leaving only the landward approach to be fortified with a bank or ditch. Hundreds of these structures are scattered around the Irish coastline, and Clare has more than its share, but each one occupies its own particular relationship with the water below it.

These coastal forts are generally associated with the Iron Age, though many continued in use across different periods, and some may have served purposes beyond simple defence, including settlement, lookout, or the keeping of livestock on ground that was difficult to reach without permission. The landward earthwork, often a single or double rampart cut across the neck of the promontory, is frequently all that survives in legible form. Wind, erosion, and centuries of Atlantic weather have a way of reducing even substantial earthworks to low, grass-covered ridges that require some patience to read in the landscape. The Ballyherragh example sits within a county where the geology shifts dramatically from the limestone plateaus of the Burren to softer, more eroded coastal edges, which shapes how these structures survive and how they are encountered today.