In a field near Oldtowndonore in County Kildare, there is a circular enclosure that has never, as far as the record shows, been excavated, surveyed at ground level, or even walked. The only evidence that it exists at all is a faint ring of discolouration visible in aerial photography, the kind of ghostly impression that archaeologists call a cropmark. Cropmarks form when buried features, such as the filled-in ditch of a long-demolished earthwork, affect how crops or grass grow above them. Ditches retain moisture, producing lusher, greener growth; compacted foundations do the opposite. From the air, particularly in dry summers when the contrast is sharpest, these differences become legible as patterns on the landscape.

The enclosure at Oldtowndonore came to light through a Digital Globe aerial photograph taken on 28 June 2018, with the detail brought forward by Anthony Murphy, who has a long record of identifying previously unrecorded sites through aerial and satellite imagery across Ireland. The circular shape measures approximately forty metres in diameter, a size broadly consistent with the ringforts and enclosed farmsteads that were built across Ireland during the early medieval period, though without excavation any dating must remain speculative. That a site of this kind could remain unrecorded until 2018 is less surprising than it might seem; cropmark sites are invisible at ground level and only reveal themselves under particular atmospheric conditions, meaning that any given summer might produce a legible image or leave the field looking like any other.