Somewhere beneath a ploughed field in Courttown, Co. Kildare, lies the ghost of a large enclosure that has not been visible to the naked eye for an unknown number of centuries. The only evidence of its existence is a cropmark captured in a single aerial photograph taken in 1970, and without that image, the site would be entirely unknown to the archaeological record.

Cropmarks appear when buried features, such as ditches or walls, affect the growth of crops above them. A filled-in ditch retains more moisture than the surrounding soil, encouraging denser, taller growth; a buried wall does the opposite. From the air, these differences in vegetation register as distinct lines or shapes, readable as a kind of shadow map of what lies beneath. In the 1970 photograph, reference CUCAP BDH 66, the cropmark traces a fosse, that is, a defensive or boundary ditch, running in three roughly equal sides to form a triangular enclosure. The estimated dimensions are approximately 120 metres on each side, making the enclosed area substantial. Triangular enclosures are relatively uncommon in the Irish archaeological landscape, where circular and subcircular forms are far more typical, and that geometric anomaly alone makes this site noteworthy. No surface trace survives today; the land remains under level tillage, and there is nothing to see from the ground.