A large rectangular enclosure lies beneath the fields of Beaconstown in County Kildare, invisible at ground level but legible from the air as a cropmark, that particular phenomenon where buried ditches and banks cause crops above them to grow at slightly different rates, tracing the outlines of long-vanished structures in pale or dark lines across a field. In this case, the cropmark reveals both the shape of the enclosure and one specific detail that archaeologists find especially useful: a fosse, or defensive ditch, running around its perimeter, and an entrance oriented to the east.

The eastward-facing entrance is worth pausing on. Across prehistoric and early historic Ireland, an eastern orientation was common for enclosures of various kinds, possibly linked to the significance of sunrise, though the precise function of the Beaconstown enclosure remains unknown. Rectilinear enclosures of this scale are generally associated with the later prehistoric or early medieval period, distinguishing them from the more numerous circular raths and ringforts that characterise the Irish countryside. The evidence here comes from a single aerial photograph, reference GB96.FZ.21, which captured the cropmark from altitude, preserving a record of something the landscape itself has otherwise absorbed entirely.