They appear as low, horseshoe-shaped mounds of burnt and fire-cracked stone, typically found close to water sources, and they date predominantly to the Bronze Age, somewhere between 1500 and 500 BC. The one at Ballyconnoe in County Clare is a quiet example of this widespread but still not fully understood type of site.

The working theory behind fulachtaí fia, developed over decades of excavation and experiment, is that they functioned as outdoor cooking sites. A trough, usually timber-lined or cut into the ground, was filled with water, and stones heated in a nearby fire were dropped in to bring the water to a boil. Meat wrapped in straw could then be slow-cooked in the trough. Experiments conducted in the twentieth century demonstrated that this method works efficiently, and repeated use over time produced the characteristic mounds of heat-shattered stone that survive as the visible monument. Some archaeologists have suggested alternative functions, including bathing, textile processing, or brewing, and the debate has not been entirely settled. What is consistent across the type is the proximity to water and the accumulation of those fractured, fire-reddened stones.