The one at Cloonnagleragh in County Mayo is a quiet example of a site type that appears repeatedly in boggy, low-lying ground near water sources. A fulacht fia, in its simplest description, is a burnt mound, the accumulated debris of a cooking or heating method that involved dropping fire-heated stones into a water-filled trough until the water boiled. Over time, the shattered, heat-cracked stones pile up into a distinctive horseshoe or kidney-shaped mound, often dark in colour from the scorching, and usually sodden from its proximity to a stream or spring.

These sites date predominantly from the Bronze Age, roughly 1500 to 500 BC, though some have yielded earlier or later material. Experiments carried out in the twentieth century demonstrated that the method is genuinely effective for cooking large quantities of meat, and various alternative uses have since been proposed, including hide-working, bathing, and textile production. Ireland has an unusually high concentration of them, with Mayo contributing a considerable number to the national total. The specific example at Cloonnagleragh remains one of many such monuments catalogued across the county, sitting in the kind of marginal, water-adjacent ground that Bronze Age communities seem to have favoured for this activity.

Because the source material for this particular site is limited, it is worth noting simply that fulachtaí fia are easy to miss without knowing what to look for. They rarely rise more than a metre above the surrounding ground, and in areas of rough grazing or light scrub they can appear as little more than a darkened, slightly raised patch of earth near a field drain or stream bank.