On the ground, there is nothing to see. No earthwork, no raised bank, no visible boundary of any kind. Yet somewhere beneath a field on the western edge of Corcoranstown in County Kildare, the outline of a circular enclosure has quietly persisted for centuries, waiting for the right conditions to give itself away.

The enclosure came to light through a cropmark captured in an aerial photograph taken on 11 July 2018. Cropmarks form when buried archaeological features alter the growth of whatever is planted above them. A filled-in ditch, for instance, holds moisture differently from the surrounding subsoil, causing the crops directly overhead to grow slightly taller or ripen at a different rate, producing a faint but readable pattern when seen from altitude. Circular enclosures of this kind are found across Ireland and often indicate the site of a former ringfort, a type of enclosed farmstead common throughout the early medieval period, roughly the fifth to the twelfth centuries. Whether this particular example dates to that era or to some other period entirely remains unknown; the cropmark alone cannot say.