They appear as low, horseshoe-shaped mounds, typically found near water, and are generally dated to the Bronze Age, roughly 1500 to 500 BC. The standard interpretation holds that they were cooking sites: a stone-lined trough was filled with water, and rocks heated in a nearby fire were dropped in to bring it to the boil. Experiments have shown the method works efficiently. The mound itself is the accumulated debris of cracked, fire-shattered stone, discarded after each use over many seasons or centuries. There is a fulacht fia recorded at Ballybeg in County Kerry, a quiet addition to this dense and widespread class of monument.

The source material for this particular site is too limited to reconstruct its specific history or physical dimensions. What can be said is that Ballybeg sits within a county exceptionally well-furnished with prehistoric remains, and that Kerry's boggy, low-lying ground near streams and wetlands provided exactly the conditions these sites seem to favour. The broken, heat-fractured stone that forms the mound is sometimes called "pot boiler" stone, a term that captures the essential mechanics: once a rock has been used to heat water, thermal stress makes it useless for a second firing, and it is simply thrown aside. Over time, enough discarded stone accumulated to create a visible landscape feature that has survived, in many cases, for three millennia or more.