They appear as low, horseshoe-shaped mounds, typically found close to water, and are generally dated to the Bronze Age, somewhere between 1500 and 500 BC. One such mound sits at Attavally in County Mayo, easy to overlook, quietly occupying ground that has gone largely undisturbed for perhaps three millennia.

The prevailing interpretation of fulachtaí fia is that they were cooking sites. The method involved heating stones in a fire and dropping them into a water-filled trough, bringing the water to a boil rapidly enough to cook meat. Over time, the cracked and spent stones were raked aside, building up the characteristic mound that survives today. Some researchers have proposed alternative uses, including brewing, hide preparation, or bathing, and the debate has not been fully settled. What is consistent across most examples is the association with wet ground and the presence of a trough, sometimes timber-lined, sometimes simply cut into the earth or clay. The Mayo landscape, with its abundance of boggy, low-lying terrain, is particularly well suited to this kind of site, and the county contains a substantial number of recorded examples.