A kidney-shaped enclosure sits in the fields around Castleroe in County Kildare, entirely invisible to anyone walking the ground. It exists, as far as most records are concerned, as a shadow in a photograph taken from the air, betrayed only by the way crops grow differently above a buried ditch.

The site came to light in August 1995, when Dr. Gillian Barrett photographed the area as part of an aerial survey. What she captured was a cropmark, the faint but legible trace left when vegetation over a buried fosse, a defensive or enclosing ditch, grows at a different rate to the surrounding field. The resulting image revealed an irregular, curvilinear enclosure with a roughly kidney-shaped outline. The detail that makes the site particularly interesting is that it is one of two conjoined enclosures in the same area, the pair sitting side by side in a configuration that suggests a more complex arrangement than a single isolated farmstead or enclosure would imply. Barrett published the findings in 2002, and the aerial photograph remains the primary evidence for what lies beneath the soil.