Somewhere beneath a field near Sion in County Kildare, a circular ditch roughly nine metres across lies buried and invisible at ground level, detectable only because of what grows above it. The feature is known as a ring-ditch, a type of monument typically associated with prehistoric funerary or ritual activity, and it survives here entirely as a cropmark, a phenomenon in which buried features cause subtle differences in soil moisture that show up as variations in crop colour and growth when viewed from the air. In this case, the ring-ditch became legible in aerial photographs taken via Google Earth on the 28th of June 2018, when the geometry of the buried ditch traced itself in the vegetation above.

Cropmarks of this kind are often the only surviving trace of monuments that were levelled by centuries of agriculture. A ring-ditch of this diameter, approximately nine metres, is modest in scale but consistent with a class of prehistoric enclosure associated with burial mounds whose above-ground earthworks have long since disappeared. The plough flattens, the centuries pass, and what remains is a ghostly circle readable only under the right conditions, typically a dry summer when crops over a ditch, which retains more moisture than the surrounding soil, grow taller or stay greener just long enough to be caught by a camera overhead. The Sion example was identified by Jean-Charles Caillère and subsequently compiled into the record by Caimin O'Brien in 2019.