At Curragh in County Galway, on a ridge set among rolling pastureland, there is an enclosure that has not been visible to the human eye for a very long time. What we know of it comes almost entirely from a cartographer's mark made nearly two centuries ago.

When the Ordnance Survey produced its first detailed six-inch maps of Ireland in 1838, surveyors recorded a subcircular enclosure on this ridge, roughly eighteen metres from north to south and thirteen metres from east to west. Subcircular enclosures of this kind are relatively common features in the Irish landscape; they are generally associated with early medieval settlement, though some are considerably older, having served as farmsteads, burial grounds, or places of local ritual. This one was noted, measured, and mapped, and then, at some point between that first survey and the present day, whatever physical trace remained at ground level disappeared entirely. Ploughing, agricultural improvement, and the slow action of grazing animals have erased thousands of such features across Ireland, leaving only the paper record where the earthwork once stood.

Today there is nothing to see at the site itself. The ridge is there, the pastureland rolls around it, and the approximate location can be identified from the old map, but the enclosure has left no visible impression on the surface. It survives only as a coordinate, a shape on an 1838 sheet, and the faint suggestion that whoever once occupied this slight rise above the surrounding ground thought the spot worth enclosing.