Somewhere beneath the fields of Grangemellon in County Kildare, a structure lies completely invisible at ground level, discernible only from the air, and only then under the right conditions. When crops grow unevenly over buried ditches and banks, they betray the outlines of what lies beneath through subtle differences in colour and height, a phenomenon known as cropmarking. It is through exactly this kind of aerial reading that an oval enclosure was identified here, its form emerging ghostlike from the farmland below.

The evidence comes from a single aerial photograph, reference GB89.O.5, which captures the cropmark of an oval enclosure defined by a fosse, the term for a broad, flat-bottomed ditch typically dug as a boundary or defensive feature. The enclosure has an entrance oriented to the south and is accompanied by an attached curvilinear annexe, a secondary enclosure running alongside the main one in a curved form. This kind of arrangement, an enclosure with a subsidiary annexe, is associated broadly with early medieval settlement in Ireland, though the precise date and function of the Grangemellon example have not been established from the aerial evidence alone. What the photograph preserves is a plan of something that has otherwise left no surface trace.