A cropmark, the differential growth of crops above buried features where disturbed soil retains moisture differently from undisturbed ground, traces the outline of a circular bank across the field. It is the kind of site that asks you to look twice, and then to look from above.

The enclosure measures approximately 35 metres in diameter, placing it within the typical range for a rath, the Irish term for a ringfort defined by an earthen bank and external ditch. These were the farmsteads of early medieval Ireland, occupied roughly between the fifth and twelfth centuries, and several tens of thousands of them are known across the island in varying states of preservation. At Knockacappul, the aerial photograph reveals the external fosse, the ditch that would originally have encircled the bank, most clearly on the eastern to northern arc, while elsewhere it has faded almost entirely from view. Whether the bank itself ever stood to any appreciable height, or was levelled at some point in the agricultural history of the land, is not recorded.