At Ballinwillin in County Cork, a ringfort once occupied a west-facing slope, its circular earthen bank enclosing a diameter of roughly forty metres. Ringforts, known in Irish as raths, were the typical enclosed farmsteads of early medieval Ireland, built between roughly the fifth and twelfth centuries and used by farming families as much for status and livestock management as for defence. This one, however, has been entirely levelled, and no visible trace of it remains above ground.

What makes Ballinwillin particularly interesting to map and record is the precision with which its disappearance can be tracked. The ringfort appears on all three editions of the Ordnance Survey six-inch maps, each successive survey capturing the same semicircular earthwork on the slope. That consistent appearance across multiple editions suggests the feature was still legible in the landscape well into the nineteenth and early twentieth centuries. At some point a north-south road was cut through the site, removing the entire western half of the enclosure. The remainder was subsequently levelled, leaving the maps as the primary evidence that anything was ever there at all.

For anyone visiting the area with an interest in this kind of archaeology, there is little to see on the ground. The value of the site lies less in what can be observed and more in what the cartographic record preserved before the earthwork was lost entirely, a reminder that the OS map series inadvertently became one of Ireland's most important archaeological documents.