A fulacht fia, sometimes spelled fulacht fiadh, is a type of prehistoric burnt mound, typically associated with the heating of water by dropping fire-heated stones into a trough; the resulting spreads of cracked, blackened stone and charcoal-rich soil are among the most commonly found prehistoric features in Ireland. At Ballynabarny, the construction of the N11 Newtownmountkennedy to Ballynabarny road scheme prompted a rescue excavation between December 2001 and February 2002, and what emerged across three separate areas was a more complex picture than a single mound in a field.

Two fulachtaí fia were uncovered within the same stretch of ground, locally known as the Long Field, lying roughly 30 metres apart. The first and larger of the two was sited beside a natural spring, which would have kept a subrectangular timber-lined trough, measuring 2.3 metres by 2 metres, naturally filled with water. Nearby, an oval pit showing evidence of burning at its base appears to have served as the stone-heating hearth, and the cluster of post-holes and stake-holes around it suggests some kind of temporary structure or windbreak once stood there. The fact that those structures seem to have been deliberately dismantled points to seasonal or short-term use of the site. The second fulacht fia, a smaller feature adjacent to what may have been a natural pond, had three troughs arranged around it, the largest measuring 4.2 metres by 2 metres. Both burnt spreads had been badly damaged by centuries of ploughing. Later farming activity also left its mark in a different way: because the same spring that served the Bronze Age site was a persistent nuisance to post-medieval farmers, successive generations cut drainage ditches and eventually laid stone drains directly over the prehistoric features in an effort to redirect the water. A field boundary recorded on the 1839 Ordnance Survey map had been removed by the 1904 edition, and the spring, no longer managed, simply reasserted itself. About a kilometre to the south, in a field called the Well Field, a third area of excavation produced four pits, three of which showed burning, along with 83 pieces of struck flint and 28 sherds of probable Bronze Age pottery from a fourth, roughly circular pit cut to a depth of 0.3 metres. Whether these features are contemporary with the fulachtaí fia to the north remained, at the time of the preliminary report, a question awaiting radiocarbon dating.