Yet the geometry is deliberate and old: this is a rath, a type of ringfort formed from an earthen bank and surrounding ditch that served as a defended farmstead enclosure during the early medieval period in Ireland, roughly between the fifth and twelfth centuries. Thousands survive across the country in various states of completeness, but each one is its own particular compromise between original intention and the slow pressure of the intervening centuries.

The Corballybane example was already legible enough to be mapped by the Ordnance Survey in 1842, where it appeared as a circular enclosure on the six-inch series. Its internal area measures 26 metres east to west, and the defining earthen bank, still standing to a height of 1.85 metres along its eastern to west-southwest arc, gives a reasonable sense of the structure's original ambition. On the southern and western sides, the fosse, the external ditch that typically accompanied such banks, survives to a depth of 1.1 metres and a width of 4 metres. The northern edge is where time and use have been less kind: a trackway cuts across that side, truncating the interior and breaking the circuit that would once have enclosed the space completely. The ground inside slopes downward toward that northern edge, which may partly explain why the trackway settled there rather than elsewhere.

The briars that now overgrow the site are doing the quiet work of preservation as much as concealment, discouraging casual disturbance while making any close inspection a matter of patience and suitable clothing.