They appear as low, horseshoe-shaped or kidney-shaped mounds, typically found beside streams or in boggy ground, and they date predominantly to the Bronze Age, roughly 1500 to 500 BC. The one at Croghtabeg in County Kilkenny is a quiet example of this widespread but easily overlooked class of monument.

A fulacht fia, sometimes anglicised as a burnt mound, is thought to represent the remains of an ancient cooking site, though some archaeologists have proposed other uses including textile processing or even bathing. The method of operation was consistent: stones were heated in a fire, then dropped into a water-filled trough, usually timber-lined and dug into the earth, to bring the water to a boil. The stones, cracked and shattered by the repeated heating and cooling, were discarded to the side, and it is these accumulated deposits of fire-cracked stone and charcoal-rich soil that form the distinctive mound visible today. Thousands of these sites survive across Ireland, particularly in low-lying or marshy areas where the water table was close to the surface, and County Kilkenny has a reasonable share of them. The Croghtabeg example sits within this broader pattern, a remnant of organised, repeated activity in the landscape during a period when such communal or domestic tasks left more durable traces than most Bronze Age life.