What betrayed its presence was a dry summer and an aeroplane. In July 1989, aerial photography revealed a cropmark, the faint but legible signature left in ripening grain or grass when buried features beneath the soil cause crops to grow unevenly. In this case, the outline of a fosse, a defensive or boundary ditch, traced a roughly oval shape approximately twenty-five metres across. Below the surface, the filled-in ditch retains more moisture than the surrounding ground, feeding the plants above it slightly differently, and in the right conditions that difference becomes visible from the air as a darker ring in the field.

The enclosure itself likely dates to the early medieval period, when ringforts and similar enclosed settlements were common across Ireland. A fosse of this scale is modest but not unusual for a small farmstead or family compound of that era. What makes the Ballygrace site particularly interesting is its context. A second circular enclosure sits roughly twenty-five metres to the north-east, and both features lie within a broader field system of apparent antiquity. The proximity of two enclosures in the same landscape suggests this was not an isolated homestead but part of a more complex pattern of land use and settlement, though whether the two were contemporary or separated by generations is impossible to say without excavation.

Nothing about this site announces itself in the landscape today. The cropmark is a phenomenon of particular seasons and particular angles of light and altitude, and the field presents no visible earthworks or surface traces. Its significance lies less in what can be seen and more in what aerial photography quietly disclosed about the depth of human activity in what now appears to be ordinary farmland.