In a tilled field near Quinsborough in County Kildare, something circular lies just beneath the surface, invisible to anyone walking past but legible from the air as a faint ring pressed into the crop. The feature is a ring-ditch, roughly twelve metres in diameter, and it betrays itself only through a cropmark, the subtle difference in colour and height that plants show when their roots encounter a buried fosse, or ditch, below. When soil above an ancient cut retains more moisture than the surrounding ground, the crop above it grows a little taller or ripens a little later, and from altitude that difference resolves into a shape.

Ring-ditches of this kind are generally understood to be the traces of prehistoric funerary or ceremonial monuments, most often the enclosing ditches that once surrounded a burial mound whose earthwork has long since been ploughed flat. Thousands of years of agriculture can reduce a substantial cairn or barrow to nothing visible at ground level while leaving the negative feature of its surrounding ditch intact in the subsoil. The Kildare example was reported by Jean-Charles Caillere, and the cropmark can be made out on aerial imagery, a quiet circle in an otherwise unremarkable tillage field.