A coastal promontory fort uses the natural geometry of a clifftop spur, where water cuts off three sides, leaving only a narrow landward neck to be defended with a bank or wall. The result is an enclosure that requires minimal effort to make formidable, and the type is found all along Ireland's western coastline, concentrated particularly in Clare and Kerry.

Promontory forts of this kind are generally associated with the Iron Age, though many remained in use well into the early medieval period, and some may have origins earlier still. The name Caherrush itself is likely derived from the Irish, with "cathair" referring to a stone fort or fortified enclosure, suggesting that the site retained enough visible presence to leave its mark on local placename memory long after any active occupation had ceased. Whether the defences here took the form of a stone wall, an earthen rampart, or some combination of both is the sort of detail that only closer inspection or excavation would settle.