It does not announce itself with a mound or a ditch or a cluster of standing stones. Instead, it betrays its presence through the crop growing above it, which responds to buried soil disturbances in ways that are invisible to anyone walking the field but legible from the air as a distinct, circular cropmark.

Cropmarks form when buried features, such as the filled-in ditches of a ringfort, the foundations of a round structure, or the cut of a long-vanished enclosure ditch, affect how deeply a plant's roots can reach. Where a buried ditch holds more moisture, crops grow taller and greener; where buried stonework or compacted earth restricts the roots, they grow more weakly. From above, especially in dry summers when these differences are most pronounced, the outline of the buried feature becomes readable in the variation of the crop itself. In this case, the circular shape was identified not by a researcher in a light aircraft but through an orthoimage, a geometrically corrected aerial photograph, sourced from Apple Maps. The site was compiled by Caimin O'Brien, working from details originally provided by Jean-Charles Caillère, and uploaded in December 2022. Beyond its shape, which is circular, and its setting, which is agricultural tillage land, little else has been formally recorded about it.

Courtlough is a townland in north County Dublin, and the field in question is ordinary working farmland, not publicly accessible in any formal sense. There is no marker, no sign, and nothing to see at ground level; the earthwork, whatever it turns out to be, exists only as a pattern in the soil and in the satellite record. The most practical way to observe it is to search Courtlough on Apple Maps and examine the available orthoimage, as the circular form is visible there. Researchers with an interest in aerial archaeology, cropmark surveys, or the distribution of prehistoric and early medieval enclosures in the greater Dublin region may find it a useful addition to a working map of the area. For anyone else, it is a reminder that the landscape keeps its own record, and that sometimes a smartphone map, examined carefully, reveals more than a field visit ever could.