A rath is a ringfort, the kind of enclosed homestead that early medieval farmers built across Ireland in their thousands, typically a single bank and ditch around a dwelling. The one at Lisduff has three. Set on the level summit of a broad, east-west ridge in gently undulating pasture, the site presents a raised circular area just 22 metres across, yet it is wrapped in a concentric arrangement of three separate banks of earth and stone, each separated from the next by a berm, the flat shelf of ground that sits between a bank and what was once a fosse, or ditch, now largely in-filled. The outermost of the three banks survives mainly on the south-west to north-west arc of the site, with only faint traces elsewhere, while the middle bank has been significantly eroded away between the north-west and north-east.

One detail lifts the site out of the ordinary: a large glacial erratic, a boulder deposited by ice-sheet movement during the last glaciation and composed of conglomerate, has been incorporated directly into the innermost bank on the western side. The block measures roughly 1.4 cubic metres, a substantial lump of stone that whoever built the rath apparently decided to work around rather than remove, folding it into the fabric of the enclosure itself. Whether this was simple practicality or something more deliberate is impossible to say now. There are two breaks in the inner bank, one to the east at about 2 metres wide and one to the south at 4 metres, but neither corresponds to an opposing gap in the second bank, which means neither is likely to represent the original entrance. That entrance, wherever it once was, is no longer recognisable on the ground.