The example at Cullagh in County Mayo is one of countless such sites that sit quietly in fields and bogland, rarely signposted and seldom visited, yet representing a form of activity that went on across Ireland for well over a thousand years during the Bronze Age.

A fulacht fia typically survives as a low, horseshoe-shaped mound of burnt and fire-cracked stone, usually surrounding a sunken trough that would originally have been timber-lined or cut into the earth. The accepted explanation, supported by experimental archaeology, is that water in the trough was heated by dropping fire-heated stones into it, and that this was used for cooking, though theories about bathing, brewing, and textile processing have also been advanced. The shattered stones, discarded after each use because rapid heating and cooling makes them crumble, gradually built up into the characteristic mound. These sites are almost always found near a water source, since a reliable supply was essential to the whole process. Mayo, with its wet ground and abundant streams, was particularly suited to this kind of activity, and the county contains a substantial number of recorded examples.