A circular cropmark roughly 37.5 metres in diameter marks the outline of an ancient enclosure, its shape betrayed not by any upstanding earthwork but by the differential growth of crops over a buried ditch beneath. Where a ditch was once cut into the subsoil, the disturbed earth retains moisture and nutrients differently from the undisturbed ground around it, and in dry conditions the crops rooted above it grow taller or lusher, tracing the original outline in living colour. The result is a ghostly ring, invisible at ground level, that only resolves into meaning when seen from altitude.

Cropmarks of this kind are a well-established means by which archaeologists identify sites that have been completely levelled by centuries of agriculture, their physical presence reduced to nothing more than a chemical signature in the soil. The enclosure at Killissane fits a type common across Ireland, a roughly circular ditched boundary that may once have enclosed a farmstead, a ringfort, or some form of enclosed settlement dating anywhere from the later prehistoric period through to the early medieval. The site sits in the north-west corner of a large field, and its northern arc has been truncated by a field boundary running from north-north-west to north-north-east, meaning part of the original circuit has been lost, likely to repeated ploughing over generations. The cropmark was identified on Apple Maps imagery by Jean-Charles Caillère and subsequently recorded by Matt Kelleher in April 2022, a reminder that aerial and satellite platforms increasingly serve as tools for locating archaeology that would otherwise go entirely unnoticed.