The site at Cloonlyon is easy to miss and easier still to misread, looking at first glance like a natural depression in poorly drained grassland. But the curve of the earthwork is too purposeful for accident, and the dimensions too consistent to be a trick of the boggy terrain.

What survives is a low earthen bank, roughly two metres wide and half a metre high, sweeping in an arc from north-north-west to east. Along the south-western side, a stream forms a natural boundary, which may have been incorporated deliberately into whatever enclosure originally stood here. A shallow internal fosse, the term for a ditch dug on the inner side of a bank, runs alongside what remains of the earthwork, suggesting the whole feature once described an oval roughly fifty metres by thirty. By the time the Ordnance Survey recorded it for the third edition of its six-inch map in 1931, the site was already reduced to a hollow, the bank and fosse reduced further still by time, water, and agricultural use. Enclosures of this kind are found across Ireland and can date from the prehistoric period through to the early medieval, when they were used variously as farmsteads, cattle enclosures, or focal points for small rural communities. Without excavation, this one resists any firmer dating.