Somewhere near the summit of a south-west-facing slope in Clogheen, Co. Kildare, there may be an ancient circular enclosure, or there may be nothing at all. The ambiguity is the point. The site exists, officially, as a cropmark, visible in a single aerial photograph, and undetectable at ground level by anyone who walked the field in 1986.

Cropmarks appear when buried features, walls, ditches, or filled pits, affect the growth of vegetation above them. In a dry summer, grass or grain over a buried ditch tends to stay greener longer, drawing moisture from the disturbed soil below, while growth over a buried wall may yellow and thin. From the air, these differences in colour and height can resolve into shapes that are otherwise completely invisible. The photograph in question, catalogued as GSAP N213, shows what appears to be a circular enclosure on the pasture slope. Circular enclosures of this kind in Ireland are frequently the remains of raths or ringforts, the enclosed farmsteads that were built in their thousands during the early medieval period, roughly between the fifth and twelfth centuries. Whether this is such a site, or something older, or simply a trick of the soil and the season, remains an open question. When someone checked the field itself in 1986, the surface gave nothing away.