In a field near Prumpelstown in County Kildare, a circular enclosure lies almost entirely invisible to anyone standing on the ground. Only from the air does it reveal itself, and even then only partially, appearing as a cropmark tracing the arc of a narrow fosse. A fosse is essentially a ditch, typically dug as a boundary or defensive feature around a settlement or enclosure, and here the buried remnant of one survives only as a difference in how the crops above it grow, the soil disturbance below causing vegetation to respond in ways that the surrounding field does not.

Aerial photography has captured roughly half of what would once have been a complete circular enclosure, with an estimated maximum diameter of around 45 metres. Circular enclosures of this kind are scattered across the Irish landscape and tend to be associated with the early medieval period, though without excavation it is difficult to assign a precise date or function to any individual example. They might represent a ringfort, a defended farmstead, or a enclosure of some other domestic or ritual purpose. What survives at Prumpelstown is a ghost of that original feature, preserved not in stone or earthwork but in the seasonal behaviour of crops responding to what lies beneath them.