What makes this particular site quietly remarkable is not just its scale, with an overall diameter of around 95 metres, but the fact that the earthworks you see today are the product of a deliberate and fairly drastic redesign carried out by the people who actually lived there.

A ringfort is an enclosed farmstead of early medieval Ireland, typically defined by one or more circular banks of earth and an accompanying fosse, the ditch from which that bank material was dug. The example at Ballynamanagh is bivallate, meaning it has two such circuits of bank and fosse. Excavations carried out in 1948 and 1949, covering roughly a quarter of the site, revealed that this double arrangement was not the original plan. In its first phase the enclosure was univallate, a single ring with an internal diameter of around 76 metres. That first phase appears to have been short-lived. Relatively soon after initial occupation began, a very deep fosse was cut inside the existing defences, and the spoil was heaped up along its inner edge to create the large inner bank that dominates the site today. The effect was to compress the usable interior down to around 48 metres across. No evidence for internal structures was found during the excavation, but well-preserved deposits of animal bone and sea-shells turned up throughout the excavated areas, along with artefacts suggesting a range of craft activities. Radiocarbon dates place the occupation somewhere between the 4th or 5th century AD and at least the 9th century. The measurements alone convey the ambition of the Phase 2 remodelling: the inner fosse drops roughly 6 metres from the top of the bank to its base, and in places reaches 9 metres across at the top, while a causeway 4.4 metres wide carries the original north-east entrance across it.

One additional detail persists by reputation rather than physical evidence. Local tradition holds that a souterrain, an underground stone-lined passage used in early medieval Ireland for storage or refuge, lies just inside the enclosure to the south-west of the entrance. No surface trace of it survives, and nothing from the 1940s excavations confirmed it. Whether the passage exists undisturbed beneath the turf, was filled in at some point, or belongs to the long life of accumulated local memory that tends to attach itself to sites like this, nobody has yet been able to say.