The reason is simple once you see the terrain: the ravine itself supplied the other half. The cliff edge did the defensive work that an earthen bank would otherwise have to do, leaving the builders to concentrate their effort on the landward arc. The result is a semicircular enclosure roughly 22 metres across, its open side facing the drop.

The surviving earthworks are modest but legible. A scarp some two metres high defines the arc, fronted by an outer fosse, a defensive ditch, about three metres wide, with traces of an external bank still readable on the northern side. A causewayed entrance, essentially a raised strip of ground left uncut across the ditch, marks the north-east approach at around four metres wide, just enough to admit people or livestock in single file while remaining easy to defend or block. Forts of this general type, using natural features as one side of the enclosure, are not unusual in Ireland, but each site makes its own particular calculation between the landscape it occupies and the effort its builders were prepared to invest. The first edition Ordnance Survey six-inch map, surveyed in the nineteenth century, already recorded this one as a semicircular enclosure, suggesting the earthworks were clear enough then to be worth noting. Quarrying has since disturbed the north-east sector of the interior, removing whatever might once have survived on that side.