The earthwork at Ballyglass is a rath, the most common type of ringfort found across Ireland, a circular enclosure defined by a raised earthen bank and an outer ditch, originally built to protect a farming family and their livestock during the early medieval period. What makes it worth attention is how much of the original structure has survived the pressures of tillage: the bank still stands to an internal height of nearly 1.74 metres, and the external fosse, a defensive ditch dug around the perimeter, remains visible along the north-western to south-western arc, still reaching a depth of around 0.8 metres.

The enclosure is broadly circular, measuring roughly 35 metres east to west and about 34 metres north to south, sitting on a west-facing slope that would have given its inhabitants a useful outlook over the surrounding land. Two gaps in the earthen bank suggest original entrance points: one to the east-south-east, around 4.5 metres wide, with a causeway preserved across the fosse to allow passage, and a second to the west, slightly wider at 5 metres. The causeway detail is particularly telling, since it indicates deliberate construction rather than later erosion or accidental damage. Ringforts of this kind were rarely purely defensive; they functioned primarily as enclosed farmsteads, and the careful management of entrances reflects the social and practical concerns of the people who built and maintained them.