In the undulating grassland of Caltragh in County Galway, a circular enclosure roughly twenty metres in diameter was once substantial enough to be mapped, yet today nothing at ground level survives to show for it. No bank, no ditch, no crop-mark visible to the casual eye. The place is, in the most literal sense, known only because someone recorded it before it disappeared.

The evidence for it comes from the first edition of the Ordnance Survey six-inch map, the great nineteenth-century cartographic project that swept across Ireland and committed to paper thousands of field boundaries, earthworks, and ancient features that were already, even then, fading from the land. What the surveyors captured at Caltragh was a circular enclosure, the kind of roughly ring-shaped earthwork found widely across Ireland and associated most often with early medieval settlement, typically a raised bank enclosing a farmstead or occasionally a burial ground. The "caltragh" place-name itself is worth noting: it derives from the Irish "calthrach", meaning a burial ground or plague pit, suggesting that whatever stood or happened here carried some significance in local memory long before the OS teams arrived with their measuring chains. The enclosure they recorded was modest in scale, about twenty metres across, sitting in ground that rolls and dips in the way of much of this part of North Galway.