At Carrowgobbadagh in County Sligo, an enclosure sits on an east-facing slope above the Ox Mountains, recorded and plotted, yet offering the visitor nothing to see. No banks, no ditches, no stones. Just pasture, a change in gradient, and a view.

The site is known primarily through cartographic evidence. It does not appear on the first edition of the Ordnance Survey six-inch map, the great nineteenth-century survey that documented Ireland's landscape in remarkable detail, which suggests it was either missed at the time or had already degraded beyond recognition by then. By the time later editions were compiled, however, something had been identified: a hachured arc, the mapmaker's shorthand for a curved earthwork or bank, is shown running from the north-east around through south to south-west. Enclosures of this general type, typically circular or subcircular earthen boundaries, are found across Ireland in considerable numbers, and many are associated with early medieval settlement, though without excavation it is rarely possible to say with confidence what any individual example was used for or when it was constructed. At Carrowgobbadagh, the arc on the map is now the only meaningful evidence that anything was ever here at all.