They appear as low, horseshoe-shaped mounds of burnt and fire-cracked stone, typically found close to a water source, and the one recorded at Lanmore in County Mayo is a quiet example of just how densely this particular type of site populates the Irish midlands and west. What they were actually used for remains a subject of genuine debate among archaeologists.

The prevailing interpretation, developed over decades of excavation and experiment, is that fulachtaí fia functioned as cooking sites. The usual method involved heating stones in a fire and dropping them into a water-filled trough, bringing the water rapidly to a boil and keeping it there long enough to cook meat. Experiments carried out in the twentieth century demonstrated that this method works efficiently, and that repeated heating and quenching causes the stones to shatter, which explains the characteristic spreads of broken, reddened rock that define these monuments. Most Irish examples date to the Bronze Age, roughly 1500 to 500 BC, though some have produced earlier or later dates. The site at Lanmore fits into this wider, ancient pattern of activity, a fragment of everyday prehistoric life preserved beneath the turf of north Connacht.

Alternative theories have accumulated over the years, including proposals that the troughs were used for bathing, textile processing, or even brewing, and it is likely that no single explanation covers every example. The sheer number of these sites, estimated at over four thousand across Ireland, suggests they served a routine and widely shared purpose, whatever that purpose ultimately was.