At Ardnacrushy in County Cork, a ringfort once occupied a south-facing slope, its circular earthen bank enclosing a space of roughly 28 metres in diameter. Today there is nothing to see. The land is under tillage, the surface entirely smooth, and no trace of the original structure survives above ground.

What we know of it comes largely from the Ordnance Survey's six-inch map of 1842, on which the site appears as a hachured circular enclosure, the cartographers' method of indicating an earthwork with sloping sides. A rath, as this type of monument is commonly called, is a ringfort formed from earthen banks and ditches rather than stone, and was typically used as a defended farmstead during the early medieval period, broadly between the fifth and twelfth centuries. Thousands were built across Ireland, and many survive in reasonable condition, particularly in areas where agriculture remained less intensive. At Ardnacrushy, the opposite happened. At some point between the mid-nineteenth century and the present, the banks were levelled, the ditches filled, and the enclosure absorbed into the surrounding farmland. The 1842 map is now the most concrete evidence that anything was ever there at all.