Somewhere beneath the farmland of Castlereban in County Kildare, the outline of an ancient enclosure survives, not as a visible earthwork but as a pattern readable only from the air. The site exists, for most practical purposes, as a ghost pressed into the soil.

The enclosure came to light in 1991, when Dr. Gillian Barrett conducted an aerial photographic survey of the area. The photographs revealed cropmarks, the subtle variations in crop growth that betray buried features beneath a field's surface. Where ditches or fosses were once cut into the ground, the soil retains moisture differently, and the vegetation above can grow taller or ripen at a slightly different rate, producing faint stripes and curves that are invisible at ground level but legible from above. In this case, the cropmarks outlined a curvilinear enclosure, roughly circular in form, with a rectilinear annexe, a squared-off additional enclosure, attached to its south-western side. Both features are defined by fosses, meaning the boundaries were originally ditched rather than built up. This combination of a rounded main enclosure with a rectangular addition is not unusual in the Irish archaeological record and may suggest a settlement or agricultural complex, though without excavation the function and date of the Castlereban site remain unconfirmed. The photographs that preserve this evidence are catalogued as GB91.EA.24 and GB91.EA.27.