No earthworks, no obvious mounds, no stones breaking the surface. The only evidence that something is there at all came from the air, in the form of a crop mark, the kind of faint patterning in growing vegetation that reveals buried features invisible at ground level. Plants rooted above old ditches or disturbed soil tend to grow differently from those in undisturbed ground, and under the right conditions, usually a dry summer when crops are under stress, these differences show up clearly enough to be photographed from a low-flying aircraft.

What those aerial photographs revealed at Barnahely is a bivallate circular enclosure, meaning a roughly circular area defined by two concentric ditches or banks rather than one. The inner diameter runs to approximately 54 metres, the outer to around 75 metres, giving a substantial enclosed space with a considerable gap between the two circuits. Enclosures of this type are broadly associated with the early medieval period in Ireland, though without excavation it is impossible to say with any confidence what this particular site was used for. The source of the crop mark image is recorded as CUCAP, the Cambridge University Collection of Aerial Photography, which holds oblique aerial photographs taken across Britain and Ireland over many decades and has contributed significantly to the mapping of buried archaeological sites.