It is the kind of feature that a walker might cross without a second thought, reading it as natural undulation in a landscape shaped by glacial drift. The drumlin ridges of Monaghan are themselves the legacy of the last ice age, long whale-backed hills of boulder clay running in roughly parallel lines across the county. But this particular summit carries the traces of deliberate human shaping: a scarp, a berm, and the ghost of a bank that aerial photography from the mid-1990s and 2000 still showed clinging to the southern and western edges.

The earthwork is classified as a fort, a term covering a broad range of enclosed sites in the Irish archaeological record, many of them associated with the early medieval period, though few can be dated without excavation. What survives at Listinny is a subcircular raised platform defined on its western side by a grass-covered scarp roughly five metres wide and just under two metres high, which gradually merges into the natural slope on the other sides. Between the base of that scarp and a field bank running from the south-southwest around to the northeast, there is a narrow berm, a flat shelf or ledge two to three metres wide, separating the two earthen features. That combination, a raised interior, a defining scarp, and a berm, is consistent with the kind of enclosed settlement or defended enclosure that appears repeatedly across the Irish midlands and north, though at Listinny the landscape has long since absorbed the structure into its agricultural fabric.