This one is remarkable for what does not. Somewhere in the rough, boggy, heather-covered land around Cuillaun in County Mayo, there may or may not be a cashel, the term used for a stone-walled ringfort, typically a roughly circular enclosure built to protect a farmstead in early medieval Ireland. The difficulty is that nobody has ever been able to find it, and there is no visible trace of it at ground level or in aerial photographs.

The site entered the official record through a personal communication from F. McCann in 1990, which led to its inclusion in the Sites and Monuments Record in 1991 and the Record of Monuments and Places in 1997, designated as a possible cashel. Yet the earlier cartographic record offers no support at all: neither the Ordnance Survey six-inch maps of 1837 nor the revised edition of 1919 show anything here. There is no local memory of a cashel in the area, and no tradition that might point toward a vanished or buried structure. The working conclusion is that the original location given to the record may simply have been inaccurate, placing a notional monument in a field where none ever stood, or at least none that can now be accounted for.