Somewhere beneath the fields of Castleroe in County Kildare, a circular ditch lies buried and invisible, betraying its presence only when seen from the air. The site is known as a ring-ditch, a term used to describe a roughly circular earthwork that typically survives as the remnant of a prehistoric funerary or ritual enclosure, the outer boundary of a low burial mound that has long since been ploughed flat. What makes Castleroe quietly remarkable is not the single feature alone, but what surrounds it: four more ring-ditches, closely spaced, forming a cluster of five in the same field.

The existence of all five sites is known entirely from aerial photography, specifically from a photograph catalogued as GB89.AG.15, in which the ditches appear as cropmarks. Cropmarks form when buried features affect the growth of overlying vegetation; a filled ditch, richer in moisture and organic matter than the surrounding subsoil, will produce a slightly taller or greener crop, tracing the outline of the original cut in the ground below. The five ring-ditches at Castleroe, recorded individually under separate monument numbers, were compiled by Dr Gillian Barrett. Such groupings of ring-ditches are not unknown in the Irish midlands and east, where prehistoric communities sometimes buried their dead in loose clusters over generations, producing what archaeologists occasionally call cemetery landscapes, though the precise date and function of these particular features remain unconfirmed without excavation.