In the summer of 2006, a photographer passing overhead captured what soil and crop had quietly preserved: the ghost of a ring, pressed into the earth and betrayed only by the way the growing plants above it behaved differently from everything around them.

What the photographs recorded is a cropmark, a phenomenon that occurs when buried archaeological features, such as filled-in ditches or compacted foundations, affect how crops grow in dry conditions. Over a buried ditch, where the soil retains more moisture, crops tend to grow taller and lusher. Over buried walls or compacted surfaces, they grow more thinly. Seen from above in the right light and season, these differences in growth draw the outlines of structures that have otherwise entirely vanished. The aerial photographs taken by Michael Moore on 16 July 2006 show exactly this: a circular form in tillage at Bonabrocka, consistent in shape with the kind of enclosed settlements that were common across Ireland from the prehistoric period through to the early medieval. Such enclosures typically surrounded a homestead or small farming community, defined by a ditch and bank that marked the boundary of a defended or organised domestic space. What survives here is not the enclosure itself but its impression, the memory of a boundary held in the chemistry of the field above it.