In a field near Prumpelstown in County Kildare, a circle lies buried in the earth, invisible at ground level and detectable only from the air. An aerial photograph, catalogued as GB99.GH.20, reveals a cropmark tracing the outline of a ring-ditch, one of those quiet signatures that the Irish landscape occasionally gives up when the conditions are right. Cropmarks form when buried features, such as the filled-in ditches of ancient enclosures, affect how plants grow above them; a ditch backfilled with looser soil retains more moisture, producing a strip of lusher or more rapidly ripening crop that shows up clearly when viewed from above, particularly during dry summers.

Ring-ditches of this kind are generally understood to be the eroded remains of Bronze Age burial monuments, most likely the encircling ditches that once surrounded low earthen mounds or barrows. Over millennia, ploughing reduces the visible mound to nothing, but the ditch, cut deeper into the subsoil, leaves a lasting impression that aerial survey can still read. Kildare's relatively flat, arable landscape has proven particularly productive territory for this kind of discovery, with many such features recorded only as cropmarks, having left no trace that a person walking the field would notice.