In a field near Roosk in County Kildare, something circular and ancient lies completely buried, invisible to anyone standing on the ground. It only becomes legible from the air, and only under the right conditions: a dry summer, when crops grow fractionally taller or greener above the lines of a filled-in ditch, tracing a ghost of the original shape in the living field.

What the aerial photograph reveals is a ring-ditch, roughly eight metres in diameter. Ring-ditches are the cropmark signatures of prehistoric monuments, most often the enclosing ditches that once surrounded a burial mound or a low earthen barrow. Over centuries, the mound itself erodes and is ploughed flat, but the ditch, once backfilled, retains more moisture than the surrounding soil, and so the crops above it respond differently. The circle endures in the biology of the field long after any surface trace has vanished. The Roosk example came to light through Google Earth aerial imagery, specifically photographs taken on the 28th of June 2018, a date that suggests the dry conditions of that summer played a role in making the cropmark legible. The detail was subsequently recorded in 2019.