These structures, known in Irish archaeology as cliff castles or coastal promontory forts, work by using the sea itself as a defensive wall. A builder in the Iron Age or early medieval period would select a headland where cliffs drop away on two or three sides, then cut off the remaining landward approach with a bank, a ditch, or a series of both. The result is a fortified enclosure requiring minimal effort to defend, where the Atlantic does most of the work. The Kilkinnikin example is one of dozens scattered along the Cork coastline, each occupying its own particular jut of rock above the water.

Promontory forts of this kind are among the more atmospheric survivals of early Irish settlement, partly because their setting tends to preserve them. Coastal erosion is a slow enemy, but it is also a selective one, and many of these sites have endured simply because there was never much incentive to plough or build over them. The Cork coast is particularly dense with examples, reflecting both the suitability of its geology and the long history of communities that looked as much to the sea as to the land behind them. The specific history of the Kilkinnikin fort, including when it was built and by whom, remains to be fully documented, but its form places it within a tradition stretching back at least two thousand years.