A small circular enclosure, somewhere between ten and fifteen metres across, sits on a level patch of ground amid otherwise undulating terrain, yet it leaves no visible trace at ground level. No earthwork, no raised rim, no hollow in the soil announces itself to anyone walking past. The only evidence that something was ever there at all is a mark on a map drawn in 1838.

That map is the six-inch Ordnance Survey sheet produced during the first great systematic mapping of Ireland, a project that recorded countless features, field boundaries, and ancient remains that were already beginning to fade from the landscape. Circular enclosures of this kind are generally understood to be the remains of ringforts, the enclosed farmsteads of early medieval Ireland, though they can occasionally indicate earlier prehistoric activity. Whatever its origins, the Ardnaboy enclosure was apparently legible enough to a nineteenth-century surveyor to be worth marking down, yet at some point between that 1838 survey and the present day it slipped entirely below the threshold of visibility. Whether it was ploughed out, gradually levelled by agriculture, or simply always too subtle to read without the surveyor's original knowledge is unclear. What remains is the outline on an old map and a set of coordinates pointing to ordinary-looking ground.