Near Castletown in County Sligo, one record exists for a site that may never have existed at all, a stone row listed on the basis of a single annotation on a map, and subsequently found to leave no trace on the ground.

A stone row, as the term suggests, is a prehistoric alignment of upright stones, a form of megalithic monument found across Ireland and Britain whose original purpose remains a matter of debate. The Castletown entry was added to the RMP in 1998, drawing on a personal communication from M. A. Timoney in 1989, who had noted a possible megalith marked at roughly this location on a Sligo Field Club map. The word "possible" does a lot of work in that sentence. When the area was physically inspected in 2003, no archaeological monument could be identified, and enquiries turned up no local knowledge of one either. The site exists, for now, as a kind of cartographic ghost, a pencilled query that was copied forward through successive records until someone went to look and found only a field.