On the edge of a plateau above the Clodiagh River in County Waterford, a roughly oval patch of grass marks out something considerably older than the fields surrounding it. This is a rath, the Irish term for an earthen ringfort, and what makes this one quietly interesting is how its builders used the landscape itself as part of the design. On the western side, where the ground drops sharply some ten metres down to the river below, no bank was needed. Nature had already done the work.

Ringforts were the dominant form of enclosed settlement in early medieval Ireland, built roughly between the fifth and twelfth centuries, typically to protect a farmstead and its inhabitants or livestock. The Ballythomas example is subcircular in plan, measuring around 46 metres north to south and 40 metres east to west, which puts it towards the larger end of the ordinary range. Where the plateau does not provide natural defence, an earthen bank survives, overgrown now but still standing up to 1.8 metres on the exterior face. Beyond that bank, on the northern to southern arc, lies a flat-bottomed fosse, the term for a defensive ditch, measuring between 4.8 and 6 metres across at the top and nearly a metre deep in places. A second, lower outer bank to the north-west has been absorbed over the centuries into a field boundary and hedgerow, a common fate for such features in a working agricultural landscape. The original entrance, just under three metres wide and accompanied by a causeway crossing the fosse, faces east, which was a conventional orientation for ringfort entrances across Ireland.

The site sits at a natural vantage point, and the severe drop to the Clodiagh on the western side remains the most striking feature of the whole enclosure. The river bank would have made any approach from that direction extremely difficult, concentrating movement and access through the single eastern entrance, exactly as the original occupants intended.