Aerial photographs reveal a cropmark, a circular area roughly 36 metres in diameter, defined by a single enclosing feature. Cropmarks appear when buried ditches or banks affect the growth of crops above them, producing subtle differences in colour and height that become clear only when viewed from altitude. On the ground, a walker crossing the field would notice nothing unusual at all.

Ringforts, known in Irish as raths when earthen, were the most common type of rural settlement in early medieval Ireland, typically dating from around the sixth to the twelfth century. Most were enclosed farmsteads, the circular bank and ditch providing a boundary for a household and its livestock. Thousands survive across the country in varying states of preservation, though many more have been erased by centuries of agriculture. The one at Ballyfarnoge sits on a north-west facing slope, a position that would have made practical sense for drainage and outlook, and its survival, even in this attenuated, invisible form, suggests the enclosing ditch cut deep enough to leave a lasting impression in the soil long after the bank above it was levelled.