What makes it quietly interesting is the layering still visible beneath the overgrowth: this is not simply a raised mound but a properly engineered enclosure, with a platform, a surrounding bank, a fosse, and an outer bank, all arranged concentrically in a pattern that would have been immediately recognisable to anyone living in early medieval Ireland.

A ringfort, or rath, was the most common settlement type in early medieval Ireland, typically enclosing a farmstead and its associated outbuildings within one or more earthen banks. The Rathbeg example is reasonably substantial: the circular platform measures around 36 metres across, with an overall diameter of roughly 60 metres taking in the full defensive circuit. That circuit consists of an earthen and stone bank, now largely worn down to a scarp about a metre high on the exterior, a fosse (a flat-bottomed ditch, here around 4.2 metres wide at the top and 1.5 metres deep), and a low outer bank. A gap of about 5 metres in the bank on the south-east side may represent the original entrance, though it has since been widened for livestock access. Other breaks in the bank on the south-west side are more likely the result of cattle poaching, the gradual erosion caused by animals repeatedly crossing or pressing against an earthwork, rather than any deliberate historic modification. The interior has suffered accordingly, with erosion from grazing leaving the central platform in poor condition, and the perimeter thickly overgrown with vegetation and trees.