A promontory fort works by letting geography do most of the defensive work: a headland or coastal spur, naturally defended on three sides by the sea or by steep cliffs, is sealed off on its landward side by one or more earthen banks and ditches. The result is an enclosure that required considerably less labour than a fully surrounded ringfort, yet offered a commanding position over the water and the approaches along the shore.

These sites are found at intervals along the western seaboard of Ireland, and most are thought to date from the Iron Age, though some were likely used or modified well into the early medieval period. The Clare coast, exposed to the Atlantic and punctuated by dramatic headlands, provided ample opportunities for this kind of construction. Lislorkan is a townland in that coastal zone, and the fort there represents a category of monument that is frequently overlooked precisely because it blends so thoroughly into the landscape. Without the earthworks to draw the eye, a casual walker might cross the line of a bank without registering it at all.