The only evidence for it comes from the air: a cropmark, the faint ghost of a circular enclosure roughly thirty metres across, picked out in an aerial photograph taken in July 1995. Cropmarks appear when buried features such as ditches or banks cause the soil above them to retain moisture differently from the surrounding ground, producing subtle variations in the colour or height of growing crops that become legible only from above. What the photograph captured was the outline of a fosse, the term for a defensive or boundary ditch, tracing a near-perfect circle into the earth.

Circular enclosures of this kind are among the most common archaeological features in the Irish landscape, and in many cases they represent the remains of a rath or ringfort, a farmstead type used extensively during the early medieval period, roughly the fifth to the twelfth centuries. The circular fosse would originally have enclosed a raised interior platform, with the excavated soil thrown inward to form a bank. Whether the Ballylegan enclosure fits that category, or belongs to an earlier or later tradition of circular boundary making, is not something the aerial evidence alone can settle. What it does confirm is that someone, at some point, went to considerable effort to define and enclose a roughly circular space of modest but deliberate dimensions in this particular corner of north Cork.