It turns out to be an overgrown and infilled gravel pit, post-dating 1700, and of no archaeological significance whatsoever. That it was investigated at all is a small lesson in how landscape features accrue a kind of unearned mystery simply by appearing on old maps.

The story begins with a hachured marking on the 1947 revision of the Ordnance Survey six-inch map. Hachuring is a cartographic convention used to suggest relief or depression in the terrain, and on older OS maps such markings were sometimes applied to earthworks, enclosures, or other features that might reward closer attention. When someone finally looked at this particular marking on the ground in 1983, what they found was considerably more mundane: a gravel pit, long since filled in and grown over, its working life belonging to the centuries after 1700. Gravel extraction of this kind was commonplace in rural Ireland, used for road-making and farm drainage, and most such pits left little trace beyond a slight hollow in a field.