At Corralough in County Galway, what the first edition of the Ordnance Survey six-inch map recorded as an enclosed area, the sort of feature that invites speculation about early settlement or industrial activity, turned out on inspection in 1984 to be a disused sand pit. Inside it, with a certain deflating tidiness, someone had planted a telegraph pole.

The Ordnance Survey's six-inch mapping project, carried out across Ireland from the 1830s onwards, captured the landscape in extraordinary detail, and enclosed features on those early sheets have long drawn the attention of researchers hoping to find field monuments, earthworks, or traces of older land use. Corralough offered none of that. The sand pit, long out of use by the time anyone came to look at it properly, had found a quiet second life as a convenient hole in the ground for infrastructure.