In a field of tillage in Boley Great, County Kildare, there is an enclosure that most people will never see with their own eyes, at least not from the ground. No earthwork survives above the soil surface. No wall, no bank, no visible boundary of any kind remains. And yet the site is legible, just not to anyone standing in it.

What gives this enclosure away is a cropmark, the faint differential in how crops grow over buried features. Where a fosse, which is a defensive or boundary ditch, was once cut into the ground and later filled back in, the disturbed, looser soil retains moisture differently from the surrounding undisturbed earth. In dry conditions, the crops above it grow slightly taller or slightly more stressed, and from the air the outline of the original ditch becomes visible as a tonal variation in the field. In this case, the aerial view reveals a large oval area estimated at roughly 75 metres across on its north-northwest to south-southeast axis and around 60 metres on its east-northeast to west-southwest axis. The fosse that once defined it has been backfilled and levelled, leaving the land apparently featureless. A second cropmark, this one outlining a rectangular enclosure that abuts the oval on its east-northeast side, may represent a later, distinct phase of activity at the same location, though its relationship to the primary enclosure has not been excavated.