The enclosure measures 38 metres in diameter, its boundary formed by an earthen bank that still rises to 1.8 metres on the interior side, with an external fosse, a defensive ditch, cut to a depth of 1.35 metres. That the whole thing remains legible in the landscape at all, beneath its heavy overgrowth, is a small and unassuming kind of persistence.

This is a rath, the Irish term for a ringfort built from earth rather than stone. Ringforts were the dominant settlement form in early medieval Ireland, roughly from the fifth to the twelfth century, and most are thought to have served as enclosed farmsteads, the bank and fosse providing a degree of protection for livestock and family rather than any serious military defence. Thousands survive across the island in varying states of preservation, though a significant number have been lost to agriculture and development over the centuries. The Farranastig example retains some telling details: a gap in the bank to the south-south-east, which almost certainly marks the original entrance, and a disused trackway that crosses the interior on a north-east to south-west axis. That trackway belongs to a much later period of use, a reminder that these enclosures did not simply freeze in time but were incorporated into subsequent patterns of land use, sometimes for centuries after they were no longer inhabited in any conventional sense.