There is an ancient enclosure near Skerries in County Kildare that you cannot see. Walk the field today and you would find only level tillage ground, with one oval patch of unusually lush grass, roughly thirty metres north to south and twenty metres east to west, hinting that something lies beneath. The enclosure itself left no upstanding trace on the surface, yet from the air, under the right conditions, the land remembers.

In 1967, an aerial photograph captured what the eye on the ground cannot detect: a cropmark, the faint differential in how crops grow over disturbed or buried soil, tracing the outline of a fosse, a defensive or boundary ditch, enclosing a large circular area estimated at around sixty metres in diameter. Cropmarks of this kind appear when buried features affect the moisture and nutrients available to plants above them, making the ancient boundaries briefly legible from altitude. The same photograph showed a soil mark pressing in from the west, and that western anomaly had already been partially recorded in a different form: the Ordnance Survey six-inch map of 1909 marks the spot as a pit or depression. What that pit or depression represents, whether natural subsidence, an earlier disturbance, or something structural, remains unresolved. The circular enclosure it adjoins could be any number of things, a ringfort, a ceremonial site, an enclosure associated with early settlement, but without excavation it remains a shape without a name.