But that modest spread of scorched debris at Ballyvareen in County Limerick is the kind of trace that archaeologists recognise immediately, because it belongs to one of the most common and most debated monument types in the Irish landscape.

A fulacht fia is, in simple terms, a prehistoric cooking or heating site. The typical method involved heating stones in a fire, dropping them into a water-filled trough until the water boiled, and using that heat to cook meat or, as some researchers have argued, to brew, process hides, or even to generate steam for bathing. The stones crack and shatter with repeated heating and cooling, and over time a distinctive mound of burnt, fragmented rock accumulates. The example at Ballyvareen was excavated under licence 06E1100 by archaeologist Mary Henry. She recorded a burnt spread measuring 9.1 metres north to south and 7.5 metres wide, surviving to a depth of just 0.19 metres, which suggests considerable truncation over the centuries. The material itself was an irregular spread of black sandy clay packed with small pieces of burnt sandstone. A sondage, which is a small exploratory trench cut into part of a larger feature to test its depth and composition, was opened on the western side, where the archaeology had been disturbed by a later furrow. That furrow ran for an exposed length of 2 metres, was roughly 0.47 metres wide and 0.09 metres deep, and was filled with dark-brown silty clay containing occasional gravels, the kind of detail that points to agricultural activity cutting across a much older deposit.

The site is recorded on excavations.ie, where Mary Henry's description was uploaded in August 2012 and compiled by Denis Power. Because fulachtaí fia are so frequently encountered during development-led excavations, the record sits within a large archive of comparable sites rather than marking Ballyvareen as an isolated curiosity. There is no visitor infrastructure here; this is a piece of the archaeological record rather than a managed heritage site. Anyone with a serious interest in fulachtaí fia as a monument class would find the excavations.ie database a more rewarding starting point than any attempt to locate the spread of black clay itself.