What makes it worth a second look is precisely that tension between survival and erosion: the outer bank still rises to around three metres on its exterior face in places, yet to the north and north-east it has been worn almost flat, and a trackway running around the south-western side long ago caused the outer ditch to be filled in along that stretch.

This is a rath, the most common type of ringfort found across Ireland, typically dating from the early medieval period, roughly the sixth to the twelfth centuries. A rath consists of a roughly circular area enclosed by one or more earthen banks with an external fosse, a word for a defensive ditch, dug to provide the material for those banks. They served as enclosed farmsteads, protecting a household, its livestock, and its stores. The Ummeraboy example is modest in scale, measuring twenty-eight metres across in both directions, enclosed by a single bank that still reaches two metres in height on its interior face. The fosse, where it has not been disturbed, survives as a shallow depression, best preserved to the south-east and south, where it still measures roughly three metres wide and about seventy centimetres deep. A causewayed entrance, meaning a gap in the fosse left unexcavated to allow crossing, faces the east-south-east, and a separate break roughly four metres wide opens to the north-north-west, though this latter gap is likely the result of erosion or later interference rather than original design.