On 16 July 2006, aerial photographs captured what is known as a cropmark, a phenomenon where buried features beneath a field cause the crops or vegetation above them to grow differently, revealing outlines that are otherwise invisible at ground level. In this case, the cropmark traced a circular enclosure roughly 20 metres in diameter, consistent with what archaeologists call a ring-ditch, the buried remains of a circular ditch that once surrounded a central area, often associated with prehistoric funerary or ritual use.

Ring-ditches of this kind are frequently the eroded remnants of round barrows, mounded burial monuments that were once a common feature of the Irish landscape but have in many cases been levelled by centuries of agriculture. The circular ditch, which would originally have defined and perhaps drained the base of the mound, is often all that survives. At Bonabrocka, even that ditch is no longer visible on the surface; it exists only as a chemical and biological signature in the soil, legible for a few weeks each summer when crop growth conditions are just right. The photographs taken by Michael Moore that July caught the site at precisely such a moment.