What gives it away is the crop itself. In dry summers, buried features such as ditches retain moisture and produce taller, greener growth, while compacted material does the opposite, and from the air these differences read as distinct bands of colour and tone across an otherwise uniform field. The result is a cropmark, a ghostly outline of something ancient, legible only from altitude and only under the right conditions.

What the aerial photographs captured, taken by Michael Moore on 16 July 2006, is a circular bivallate enclosure, meaning one defined by two concentric ditches or banks rather than a single boundary. The estimated external diameter runs to roughly 60 metres. Enclosures of this kind are generally associated with the early medieval period in Ireland, though some have earlier origins, and the presence of two circuits rather than one is often taken to indicate a site of some significance, whether a high-status settlement, a place of ritual, or a boundary that needed reinforcing. At Dunganstown, no excavation has been recorded that would confirm the date or function of this particular example. It exists, for now, as a shape in the soil, known only because one summer afternoon the conditions were right and someone happened to be looking.