They appear as low, horseshoe-shaped mounds, typically beside a stream or in boggy ground, and are thought to date predominantly from the Bronze Age, roughly 1500 to 500 BC. The working theory is that stones were heated in a fire, then dropped into a water-filled trough to bring it to the boil, though what exactly that boiling water was used for, whether cooking, textile processing, bathing, or something else entirely, remains a matter of genuine archaeological debate. The one at Killulla, in County Clare, is a quietly unremarked example of this widespread but still mysterious monument type.

Clare has a dense concentration of prehistoric remains, and fulachtaí fia are well represented across the county, often turning up in low-lying or marginal ground that was never subsequently built over or deeply ploughed. Killulla itself is a townland in the west of the county, and the presence of a fulacht fia there fits a broader pattern of Bronze Age activity in the Burren and its fringes, a landscape where thin soils and exposed limestone made certain kinds of farming difficult but did not deter human settlement. The charcoal-rich, burnt stone that fills these mounds preserves well in waterlogged conditions, which is part of why so many have survived at all.