In a field near Aylmerstown in County Kildare, the ground holds the faint outline of a circle that is almost entirely invisible to anyone walking across it. The only way it has ever been clearly seen is from the air, where the differential growth of crops betrays the presence of something buried beneath, a phenomenon known as a cropmark. The circle in question traces what was once a fosse, or enclosing ditch, roughly twenty-five metres across at its widest point.

The feature is interpreted as either a ring-barrow or a ring-ditch, two closely related monument types that belong broadly to prehistoric funerary tradition. A ring-barrow typically consists of a low central mound enclosed by a circular ditch and sometimes an outer bank, while a ring-ditch is the term used when only the ditch itself survives, the mound having been levelled by centuries of ploughing and agricultural activity. Both forms are associated with burial and ritual, and examples are found across Ireland and Britain from the Neolithic through to the early Bronze Age. The aerial photograph that first recorded this particular site, catalogued under the Cambridge University Collection of Aerial Photography, also reveals a second related site positioned just to the west, suggesting that this may have once been a small cluster of monuments rather than an isolated one.