A circular enclosure, the kind of boundary feature that in Ireland can signal anything from an early medieval farmstead to a prehistoric ritual space, shows up clearly on aerial imagery, its outline traced by subtle differences in soil, crop growth, or vegetation. Yet when investigators walked the terrain in July 1987, they found nothing at surface level, no earthwork, no raised bank, no trace of a boundary that the camera had seemed so certain about.

This is not as unusual as it sounds, though it remains quietly compelling. Aerial photography has long been one of archaeology's more reliable tools for detecting features that centuries of ploughing, weathering, or simple neglect have reduced below the threshold of direct observation. A buried ditch or a filled-in bank can still influence what grows above it, creating a cropmark or soilmark that the human eye at ground level cannot resolve but that becomes legible from altitude. The enclosure at Knockmore falls into this category: present enough to register on the aerial record, gone enough that the hillside gives nothing away to a visitor standing on it. What the photograph captured was effectively a ghost of a boundary, its physical substance spent but its geometry somehow preserved in the chemistry of the soil.