In a field in Hobartstown, County Kildare, something circular lies beneath the soil, invisible at ground level but legible from the air. Aerial photographs reveal a cropmark, the faint but distinctive signature of a buried ditch, tracing out a roughly circular enclosure no more than fifteen metres across. Cropmarks form when buried features affect how plants grow above them; a filled-in ditch retains more moisture than the surrounding soil, so the crops rooted above it grow taller or ripen at a slightly different rate, producing a contrast that becomes visible from altitude even when nothing can be seen on the surface.

The feature is interpreted as a ring-barrow or ring-ditch, a class of monument associated broadly with prehistoric funerary practice. A ring-barrow typically consists of a low central mound surrounded by a circular ditch, a fosse, sometimes with an outer bank. They are found widely across Ireland and Britain and are generally understood as burial monuments, though their precise use varied considerably across time and region. The example at Hobartstown is small, with an estimated maximum diameter of around fifteen metres, and what remains is essentially the ghost of the enclosing ditch, recorded in aerial photographs taken as part of the Cambridge University Collection of Aerial Photography.