The enclosure is a cashel, the term used for a ringfort built of stone rather than earth and timber, and in the Irish landscape these structures typically date from the early medieval period, serving as farmstead enclosures for a family and their livestock. This one sits on a gentle east-west ridge where grassland meets bog, ringed so thickly by hazel and blackthorn that the scrub has begun to push inward across the interior. The outer face of the wall has slumped and spread in places into a broad rubble scatter, augmented over the years by field clearance stones heaped against it, while the inner face remains comparatively intact, still standing to somewhere between 0.9 and 1.25 metres depending on where you measure it. A large recumbent boulder rests against the exterior on the northern side, its purpose unrecorded.

The second history is quieter and more affecting. The flat interior was used at some point as a cillín, a children's burial ground. These informal graveyards, often sited at prehistoric or early Christian enclosures across Ireland, were used for the interment of unbaptised infants, who were excluded by Catholic doctrine from consecrated ground. The practice persisted in rural Ireland well into the twentieth century, and the choice of an existing ancient enclosure was common, lending a kind of borrowed sanctity to ground that the Church would not recognise. No graves are now visible inside the cashel at Tawnaghbeg, though the association is recorded. Later field walls radiate outward from the structure to the north, south-east, and south-west, suggesting the enclosure became a convenient anchor point for the reorganisation of surrounding land long after its original use had ended, the monument absorbed quietly into the working geometry of the townland.