When archaeologists excavated a rath at Lislackagh in County Mayo ahead of the construction of the N5 Swinford by-pass, they found not just the enclosure itself but evidence of iron-smelting activity tucked into its southern half. A rath, for those unfamiliar with the term, is a ringfort, typically a circular earthen enclosure used as a farmstead during the early medieval period. That one should contain an iron-working furnace is not unheard of, but it is far from common, and the find adds a layer of industrial complexity to what might otherwise have seemed a straightforward rural settlement.

The furnace was a pit-type, meaning the smelting took place in a pit dug into the ground rather than in a freestanding structure above it. It was fully excavated in 1992 and 1993 as part of the advance works for the by-pass, and the associated finds told a coherent story: furnace bottoms, the glassy slag residue that collects at the base of a smelting pit during the reduction of iron ore, and smelted but unforged iron, suggesting the site was producing raw iron rather than finished objects. The metal had been extracted from ore but not yet worked into tools or weapons. Whether a smith elsewhere completed that process, or whether the operation was simply interrupted at some point, the finds alone cannot say.