In a field in Baronsland, County Kildare, there is a monument that most people walking past would never see. It appears not as a mound or a wall or any surface feature at all, but as a faint circular mark in the soil, roughly six metres across, detectable only from the air. What looks like ordinary farmland from the ground gives itself away, from altitude, as the site of something far older.

The feature is a ring-ditch, a type of site typically associated with prehistoric funerary or ritual activity. Ring-ditches are the buried remains of circular ditches, often all that survives of a round barrow or burial mound once the earthen mound itself has been levelled by centuries of agriculture. They show up as cropmarks, a phenomenon where buried ditches or pits, retaining more moisture than the surrounding soil, cause the vegetation directly above them to grow differently, usually slightly taller or greener, in a pattern that mirrors the shape of whatever lies beneath. On satellite and aerial photography, particularly during dry summers when the contrast between soil types is most pronounced, these ghost outlines can be remarkably clear. The Baronsland example, approximately six metres in diameter, was identified through aerial photography of precisely this kind.