That fosse, a defensive ditch, was almost certainly carved to make the headland into an island at high tide or in attack, turning the promontory into a natural fortress. But the castle itself may be the younger occupant here, built over or beside earthworks that already existed long before any medieval stonework arrived.

Researchers Grogan and Kilfeather noted in 1997 that the castle site may overlie an earlier promontory fort, a type of enclosure, typically Iron Age, that uses the natural cliff edges of a headland as its primary defence and closes off the landward side with a bank and ditch. Casey, writing in 2001, identified an earthen rampart roughly 55 metres to the west of the promontory, enclosing a broadly rectangular area, and considered it likely to predate the castle. The same survey noted modern gaps cut through this bank, and at a point around 12 metres from the northern cliff edge, one of those gaps revealed what appears to be a collapsed and grassed-over hut site within the bank itself. A shallow external fosse, approximately 7 metres wide, and a further outer bank were also intermittently visible near the northern cliff edge, suggesting a more elaborate defensive arrangement than the surviving landscape immediately betrays.

What the site offers, for anyone who takes time to look carefully across the grassland rather than simply towards the castle ruin, is a landscape that has been shaped, reshaped, and partially erased across several different periods. The hut remains within the bank, barely legible now under turf, and the interrupted line of the outer fosse close to the cliff are the quieter details that repay a slower kind of attention.