The rath at Ballynidon, on the northern side of a ridge in County Cork, belongs to this category. A rath is a type of ringfort, a roughly circular enclosure defined by an earthen bank and ditch, typically associated with early medieval settlement and farming. This one measured approximately 30 metres in diameter, a modest but not unusual size, and today there is no visible surface trace of it whatsoever.

What we know comes almost entirely from cartographic evidence. The Ordnance Survey's six-inch map of 1842 recorded the site with hachuring, the system of short lines used by early OS surveyors to indicate an earthwork or enclosure, suggesting the feature was still legible in the landscape at that point. By the time the revised six-inch map was produced in 1904, only the northern bank was indicated, hinting that the enclosure was already diminishing. Sometime in the intervening century, whatever remained was lost entirely, likely to agricultural levelling. There is also a possible second ringfort recorded approximately 220 metres to the east, raising the intriguing if unanswerable question of whether the two were ever contemporaneous parts of the same early medieval farmstead or landholding.