It is about twelve and a half metres across and just a metre high, and to an untrained eye it could pass for a natural rise in the ground. It is, in fact, a fulacht fia, one of the most common yet persistently puzzling monument types in the Irish archaeological landscape. These mounds are composed almost entirely of burnt and fire-cracked stone, the accumulated debris of repeated heating. The accepted explanation is that stones were heated in a fire and then dropped into a water-filled trough, bringing the water rapidly to the boil. What the troughs were actually used for, whether cooking, textile processing, bathing, or something else entirely, remains a matter of ongoing debate among archaeologists.

Fulachtaí fia are found in their thousands across Ireland, and the majority cluster near water, as this one does on the southern bank of a stream. They date broadly to the Bronze Age, though some have produced dates extending into the Iron Age. The mound at Ballygibbon follows the classic form: a horseshoe or roughly circular heap of shattered, heat-stressed stone that built up over years or centuries of use, gradually accumulating into a feature substantial enough to survive millennia of farming and weathering. The fact that this example sits in marshy ground is typical of the type; the same waterlogged conditions that make such land difficult to cultivate have also helped preserve the mound from disturbance.