Less remarked upon is a smaller, quieter feature of the same landscape: an inland promontory fort that used the natural lie of the land as its primary defence, rather than any dramatic clifftop setting. Promontory forts are usually associated with coastal headlands, where builders cut a fosse, or ditch, across a narrow neck of land and let the sea do the rest of the defensive work. Here, the same principle was applied inland, with the rivers playing the role the sea might otherwise fill.

The fort occupies a roughly circular area approximately 63 metres in diameter. Its enclosure is defined on the northwest to southeast side by a scarp, an artificially cut or enhanced slope, fronted by an external fosse. On the south-southeast to north-northwest side, the builders relied on the natural scarps dropping down to the River Boyne and a small tributary, letting the water-cut terrain provide what the ditch provided elsewhere. An entrance with a causeway crosses the fosse at the northeast, giving controlled access to the interior. The arrangement was documented by O'Kelly in 1978, and it sits within a broader landscape that has been occupied, modified, and contested since at least the Neolithic period. The choice of this particular spur of ground, where two watercourses effectively isolated a tongue of land, reflects a practical logic that would have been obvious to anyone who knew the river's behaviour across the seasons.