Some mark a place where something wasn't. At Kilmacowen in County Sligo, a site was catalogued first as an enclosure in 1989, then reclassified as a midden in 1995, a midden being a prehistoric refuse heap, typically composed of shells, animal bones, and other domestic waste, which can offer archaeologists a remarkably detailed picture of how early communities lived and ate. The problem is that when someone finally went to look, there was nothing there.

The original source of the information is unknown, which is itself an unusual circumstance. Archaeological records generally trace back to a fieldworker, a local informant, an antiquarian account, or an older map annotation. Here, the chain of evidence simply stops. The site appeared under one category in the Sites and Monuments Record of 1989, shifted to a different category in the Record of Monuments and Places six years later, and then, when the area was physically inspected in 2014, neither feature could be identified on the ground. The record now sits in a kind of official limbo, acknowledged but unverified, pending any future evidence that might revive it as a genuine monument.