Where a typical ringfort, the circular earthwork enclosure common across early medieval Ireland, relies on a continuous bank to define and protect its interior, this one stops short. The northern boundary is not built at all. Instead, the ground simply drops away in a sharp, cliff-like fall above a stream, and the fort's builder apparently decided that nature had already done the work.

What the builder did construct survives as a roughly semicircular arc of earthen bank, rising to about 1.75 metres in height, running from the south-east around to the west. On the outer side of this arc there is a shallow fosse, the term for a defensive ditch dug to complement a bank, adding a modest additional obstacle between any approach and the enclosed area. Together, the bank and fosse complete the circuit that the natural drop to the north begins. The result is an enclosure whose shape is determined as much by geology as by human intention, the stream cutting the boundary just as deliberately as any spade. Exactly when it was built, and by whom, the surviving evidence does not say.