Somewhere among them, at Kilbaha, sits a coastal promontory fort, a type of prehistoric or early medieval enclosure that used the natural geometry of a headland as its primary defence. The builders would have cut a ditch or raised a bank across the narrow neck of land connecting the promontory to the mainland, letting the sheer cliff edges do the rest of the work. The sea, in effect, became the wall on three sides.

Promontory forts of this kind are found all along the Atlantic seaboard of Ireland, and their dates vary considerably. Some belong to the Iron Age, others to the early medieval period, and many remain unexcavated and therefore undated. They are thought to have served a range of purposes, from defended farmsteads to refuges in times of raiding, and their clifftop positions suggest a population that was as alert to threats arriving by sea as by land. The Kilbaha example occupies a stretch of coastline that would have given its occupants a commanding view over the lower Shannon estuary and the open ocean beyond, a position that would have had obvious strategic value at almost any point in the past two thousand years.