This is a rath, a type of ringfort that was once among the most common settlement forms in early medieval Ireland, typically enclosing a family farmstead within an earthen bank and an outer ditch known as a fosse. The example at Ballynacor measures roughly 31 metres east to west, with a wide external fosse that still traces much of its original circuit. A modern field fence has been laid along the line of that fosse between the south-east and south-west, quietly following the logic of a boundary that may be well over a thousand years old.

The site occupies a position that would have offered its inhabitants a degree of natural defence, set as it is on a ridge, though the views from here are described as restricted rather than commanding. That combination, elevated ground but not prominently exposed, is fairly typical of the pragmatic site selection seen across Irish ringforts, where proximity to workable land often mattered as much as visibility. A possible entrance gap, approximately 3.3 metres wide, survives at the north-north-east, which is a common orientation for such openings. Thousands of raths survive across Ireland in varying states of preservation, but many have been levelled by ploughing or erased by development; the fact that this one retains its bank and fosse, however reduced, gives it a quiet coherence.