What exists at Tullamaine in County Kilkenny is a circle that only becomes legible from the air, and only under the right conditions, when a dry summer draws the ghost of an ancient boundary up through the soil in faint differences of colour and growth.

The site was identified from a cropmark recorded in an aerial photograph taken on 22 July 1963, part of the Cambridge University Collection of Aerial Photography. Cropmarks form when buried features, such as a fosse, which is essentially a defensive or boundary ditch, affect the vegetation above them. A filled-in ditch retains more moisture than the surrounding ground, encouraging slightly lusher or taller crop growth along its line; in a dry season, that difference becomes visible from altitude as a distinct mark in the field. At Tullamaine, this process revealed a sub-circular enclosure roughly thirty metres in diameter, the probable outline of a fosse that once defined some kind of enclosed space. The land was under tillage when the photograph was taken, which is precisely the agricultural condition that makes such marks most legible. What the enclosure originally contained or who built it remains unknown from the available evidence, though sub-circular enclosures of this general scale are a common feature of the Irish archaeological landscape, associated in many cases with early medieval settlement or activity.