Roughly twenty-five metres across, the feature is defined by a low scarp at its edge, and when it was inspected on the ground in 1998, a ring of unusually dense vegetation around the perimeter hinted at something older beneath: the ghost of a fosse, the type of encircling ditch commonly dug to define and defend early settlement sites. Neither the 1840 nor the 1916 Ordnance Survey six-inch maps show anything here, and it did not appear in the Record of Monuments and Places when that register was compiled in 1996. Its existence only came to wider attention when satellite imagery captured it clearly in 2020.

The absence from two centuries of mapping is what makes Knocknaskeagh quietly puzzling. Enclosures of this kind, broadly circular and ranging from modest farmsteads to more substantial settlement sites, are a familiar feature of the Irish landscape, usually dating from the early medieval period. They are typically defined by an earthen bank and an outer ditch, or fosse, the spoil from digging one often used to raise the other. At Knocknaskeagh, the bank has been reduced to a scarp and the fosse appears to survive only as a change in the soil, expressed in the way vegetation grows above it. The site sits about thirty-five metres south of a stream, on elevated ground with open views in several directions, a positioning consistent with how such enclosures were typically sited. That it avoided documentation for so long, despite sitting in ordinary grazing land, is a reminder of how much of the early medieval countryside remains unregistered.