At Carrowkeel in County Sligo, an oblique aerial photograph picked out what looked like an oblong enclosure on a gentle east-facing slope in undulating pasture. It was the kind of cropmark or shadow that excites surveyors and archaeologists alike, suggesting a buried or degraded boundary, perhaps the remnant of a settlement, a field system, or an early enclosure of the sort that dots the Irish countryside.

When the location was visited on the ground, however, the picture became considerably less certain. What the aerial image appeared to show as an enclosure resolves, at close quarters, into a low and roughly oval rise, measuring approximately 27 metres east to west and 22 metres north to south, with gently sloping sides and a fairly level top. The working conclusion is that this feature is a naturally-occurring low hillock or ridge rather than anything made by human hands. It does not appear on any edition of the Ordnance Survey six-inch map, which itself tells a small story: the OS surveyors of the nineteenth century, meticulous as they were, saw nothing here worth marking, no wall line, no earthwork, no trace of occupation.