On a patch of level, poorly drained grassland at Ballinlass in County Galway, nothing is visible above ground except a shallow circular hollow roughly nine metres across. No bank, no ditch, no stonework. Just a slight depression in a wet field, and an open question.

The third edition of the Ordnance Survey six-inch map, published in 1932, recorded something rather more substantial here: a small circular mound approximately fifteen metres in diameter. Circular mounds of this kind can represent a range of things in the Irish landscape, from prehistoric burial monuments to the remains of a ringfort, a type of enclosed farmstead common from the early medieval period. But when fieldwork was later carried out at Ballinlass, no surface trace of any mound could be found. What remained was only that small hollow, which might itself be a faint echo of the feature once mapped, or might simply be an unremarkable dip in the ground. The possibility that the original cartographic record was an error has not been ruled out.

It is a reminder that maps are interpretations as much as records, and that nineteenth and early twentieth century OS surveyors, however careful, occasionally logged features that later proved ambiguous or untraceable. Whether the mound at Ballinlass was ever real, and if so what it once was, remains genuinely unresolved.