When construction crews began preparing the route of the N8 Glanmire-Watergrasshill Bypass in 2001, excavations at Trantstown in County Cork revealed a pair of iron-smelting furnaces sitting side by side, almost certainly used around 270 BC, give or take a few decades. They are small, unassuming features in the landscape, but together they represent a moment of early industrial activity in the Irish countryside that would otherwise have passed entirely unnoticed.

The two furnaces were clay-lined and positioned close together, the smaller one to the north-west measuring roughly 42 centimetres across and 36 centimetres deep, with what appear to be flues extending from its north and south sides. Its interior had filled with a hard black mass of solidified iron slag mixed with charcoal, the residue of a smelting process. The larger furnace to the south-east, about 55 centimetres in diameter, was found in a particularly well-preserved state, its clay lid still in place. Beneath that lid, layers of slag-rich material, black silty deposits, and a mixed clay-and-slag fill were stacked one on top of another, and the excavator, Sherlock, noted that the layering around the sides and base suggested the furnace had been put back into use at least once after its original firing. Both furnaces had been used to process bog iron, a naturally occurring form of iron oxide that accumulates in waterlogged ground and was a common source of raw material for early Irish smiths, who would smelt it down to extract workable metal. The radiocarbon date of 2220 plus or minus 40 BP places the activity firmly in the Iron Age. Adding further weight to the picture, two other metalworking sites were excavated nearby along the same bypass route, one roughly 530 metres to the south-west and another about 900 metres in the same direction, suggesting this part of Cork was home to a small but sustained tradition of iron production during that period.