They appear as low, horseshoe-shaped mounds, typically found near water, and are thought to represent Bronze Age cooking sites, though theories about their use have ranged from brewing to textile processing. The basic principle is well understood: stones were heated in a fire and then dropped into a water-filled trough, bringing it rapidly to a boil. Over repeated use, the heat-shattered stone accumulated into the distinctive crescent mound that survives today. The example at Lisnolan, in County Mayo, is one such site, sitting within a county that holds a remarkable concentration of prehistoric remains.

Mayo's landscape has been shaped by millennia of human activity, and fulachtaí fia are found throughout the county, often in low-lying or boggy ground where water was reliably close at hand. The survival of these monuments in the west of Ireland owes much to the preservation qualities of peat, which can seal archaeological material for thousands of years. Most fulachtaí fia date to the Bronze Age, roughly between 1500 and 500 BC, though some sites have produced dates outside that range. The Lisnolan site joins a wider pattern of such monuments across the parish and townland, part of the invisible infrastructure of prehistoric daily life that rarely draws attention but points to sustained settlement and activity in the area over a very long period.