In a field east of St Doulagh's Church in north County Dublin, a circular feature roughly twenty metres across is entirely invisible to anyone standing on the ground, yet overhead it becomes legible, written into the soil itself. This is a ring-ditch, and the only reason we know it is there at all is because of what the earth does to the crops growing above it.

The feature was first recorded in an aerial photograph taken in 1971, catalogued as FSI 450/449. What the camera captured was a cropmark, the faint but readable trace left when buried archaeology interrupts how plants grow. A ring-ditch is typically a circular or near-circular trench cut into the ground in prehistory, often associated with burial monuments or enclosures; the ditch fills over centuries with looser, more moisture-retentive soil than the surrounding ground, and the crops rooted above it grow fractionally taller or ripen at a different rate, producing a discolouration visible only at altitude. The site sits in low-lying terrain currently under tillage, and subsequent aerial imagery, including coverage visible on Bing Maps as recently as 2015, as well as imagery provided by Jean-Charles Caillère via Apple Maps and Google Earth, has continued to show the cropmark. The record has been compiled and revised by a number of researchers, most recently updated by Caimin O'Brien in December 2022.

Because there is nothing to see at ground level, a visit to this site is more of a conceptual exercise than a conventional heritage outing. The church of St Doulagh nearby is the useful landmark; the ring-ditch lies in the agricultural ground to its east. The cropmark is most likely to be legible in aerial imagery during a dry summer, when moisture stress in the soil amplifies the differential growth that betrays buried features. Anyone curious enough to look should consult the georeferenced aerial imagery available through platforms such as Google Earth or Bing Maps rather than expecting anything underfoot. The field is working farmland, and the monument, for now, remains undisturbed beneath it.