They appear as low, horseshoe-shaped mounds, typically found near water, and are generally dated to the Bronze Age, somewhere between 1500 and 500 BC. The prevailing theory is that they were cooking sites: a trough dug into the ground and lined with wood or stone would be filled with water, and rocks heated in a nearby fire would then be dropped in to bring the water to a boil. The crescent of scorched, shattered stone that built up around the trough over repeated use is what survives today as the mound. The one at Treanrevagh, in County Mayo, is one such site, quietly present in the landscape without drawing particular attention to itself.

What is striking about fulachtaí fia as a category is how ordinary they seem once you understand the mechanics, and yet how much remains genuinely unresolved. Some archaeologists have proposed alternative uses, including textile dyeing, bathing, or the brewing of ale, and experimental archaeology has shown that the water-heating method works with considerable efficiency. Mayo, with its wet boggy ground and abundant surface water, is well suited to this kind of monument, and Treanrevagh sits within a county that has yielded numerous examples across different townlands. The townland name itself, derived from the Irish, suggests a landscape that has been named and known for a very long time, layered with use across different periods.