This is a rath, the most common type of ringfort found across Ireland, typically consisting of a raised circular area enclosed by one or more earthen banks and ditches. Here, that enclosure measures approximately 27 metres east to west and 25.5 metres north to south, defined not by an intact bank but by a scarp, a cut or slope in the ground, rising to a maximum height of around 1.9 metres at its tallest point.

Ringforts were built predominantly during the early medieval period, roughly between the fifth and twelfth centuries, and served as enclosed farmsteads for a single family or small community. The bank, when intact, would have supported a timber palisade or hedge, creating a defensible boundary around a domestic space that likely contained a house, outbuildings, and perhaps animal pens. At Derrymihin, that bank no longer survives in full. Large boulders remain visible along the western, north-western, and northern edges of the enclosure, and local tradition holds that stones were removed from the embankment over time and repurposed for building field fences nearby. It is a familiar story across Ireland, where the raw material of ancient monuments proved too useful to leave undisturbed. The boulders that remain give a sense of the original scale of the structure, even as the earthwork itself has been worn down by livestock, weather, and the slow pressures of agricultural life.