Walk across the ground and you would notice nothing at all; the circle leaves no ridge, no depression, no surface trace. It only becomes visible from the air, where differential crop growth, fed by buried soil disturbances, traces a rough circle of about forty metres in diameter. Cropmarks of this kind appear when buried features, ditches, walls, or pits, affect the moisture and nutrients available to growing plants above them, causing the crop to ripen or colour at slightly different rates and so reveal the hidden geometry below.

The circle at Foulkscourt was first identified on an aerial photograph taken in 1967 and confirmed again on a later photograph from 1995. Its age and precise function are not recorded, though roughly circular enclosures of this kind are associated with a broad sweep of Irish prehistory and the early medieval period. A detail from the first edition Ordnance Survey six-inch map, surveyed in 1839, adds a minor complication: an irregular quarry appears to have been dug into the north-eastern quadrant of what would later be identified as the enclosure's footprint. That quarry has since been back-filled and is no longer traceable on the surface, meaning it may have disturbed whatever archaeology survives in that portion of the monument. A field boundary that once crossed the south-eastern sector of the site, visible on the aerial photographs, has also since been removed, leaving the field more open than it once was, though the enclosure itself remains just as invisible as before.