No earthwork rises from the field, no ring of stones interrupts the grass, and a visitor standing on the spot would have no reason to pause. What makes it a site at all is a single aerial photograph, taken on the 8th of April 1974, in which the cropmarks or soil patterns of a buried enclosure briefly declared themselves to the camera.

An enclosure, in the archaeological sense, is a broadly circular or oval area defined by a bank, ditch, or wall, and they appear across Ireland in enormous numbers, associated with everything from early medieval farmsteads to prehistoric ritual use. The one at Mertonhall was identified from that 1974 aerial survey and duly recorded, first in the Sites and Monuments Record in 1992 and then in the Record of Monuments and Places in 1998, where its status was quietly downgraded to "possible site". A subsequent field inspection found nothing visible at ground level. The enclosure, whatever its age or purpose, has been absorbed back into the land, leaving only its outline on a decades-old photograph as evidence that something was once there.