It might indicate an ancient ringfort, a collapsed souterrain, or something far more prosaic. In the townland of Castle in County Galway, one such marking on the 1930 edition of the Ordnance Survey six-inch map turned out to belong firmly in the latter category.

When the site was inspected in 1984, the feature proved to be a disused gravel pit, defined by a large, roughly circular hollow in the ground. Its date is thought to fall somewhere in the nineteenth or twentieth century, placing it within the long tradition of small, localised extraction that supplied road-making and building work across rural Ireland. Gravel pits of this kind were rarely documented with any precision; they were functional holes, dug when needed and abandoned when exhausted, which is partly why one could sit on a map for over half a century looking, to the uninitiated eye, like something archaeologically significant.