In a field near Prumpelstown in County Kildare, something circular and ancient lies just below the surface, invisible to anyone walking past but legible from the air. Aerial photographs reveal a cropmark tracing the outline of a fosse, which is a shallow ditched enclosure, forming a near-perfect circle with an estimated maximum diameter of around ten metres. That is a remarkably small area, roughly the footprint of a modest living room, and it is that scale more than anything else that gives the site its quiet peculiarity.

The cropmark itself is the only surviving evidence of the feature. Cropmarks appear when buried ditches or banks alter the moisture and nutrient levels in the soil above them, causing the vegetation to grow at a slightly different rate or colour, differences that become readable in aerial photography taken under the right conditions. The fosse recorded at Prumpelstown is thought to define either a ringbarrow or a ringditch, two closely related monument types associated with prehistoric funerary or ceremonial activity. A ringbarrow typically consists of a low mound enclosed by a ditch, while a ringditch is the ditch alone, the mound having eroded or never been raised to any significant height. Given how little survives at ground level, distinguishing between the two here is not straightforward.