Others exist only as a ghost in a summer photograph, detectable for a few weeks of the year when the crops grow unevenly over buried ground. The enclosure at Ballylegan in north County Cork belongs firmly to the second category. Its presence was confirmed from the air in July 1989, when a faint cropmark revealed the outline of a circular fosse, the ditch that would originally have enclosed or defined the site, measuring roughly thirty metres in diameter.

Cropmarks of this kind appear when buried features such as ditches or walls affect how vegetation grows above them. Filled-in ditches retain more moisture and nutrients, so the crops or grass over them tend to grow taller or greener, tracing the shape of the original cut in the soil. The Ballylegan enclosure appeared as exactly this kind of shadow, recorded as part of the Cork Aerial Survey and Archaeological Photography programme in the late 1980s. What makes it particularly interesting is its relationship to a nearby ringfort, a type of enclosed farmstead common in early medieval Ireland, typically surrounded by one or more earthen banks and ditches, which sits immediately to its south-south-east. Whether the enclosure is contemporary with the ringfort, or belongs to a different period entirely, is not established, but the two features in proximity suggest this patch of north Cork farmland was organised and occupied in some deliberate way over a considerable span of time.