To an untrained eye it might read as nothing more than discoloured soil, but this crescent-shaped mound is the remains of a fulacht fia, one of the most common prehistoric monument types in Ireland and one of the most quietly puzzling.

A fulacht fia is the archaeological trace left by an ancient cooking, or possibly bathing and brewing, site. The typical arrangement involved a timber-lined trough dug into the ground near a water source, a hearth for heating stones, and the repeated cycle of dropping those heated stones into the trough to bring water to the boil. Over time, the stones shattered from thermal shock and were discarded to either side of the trough, building up the characteristic horseshoe mound of burnt and broken material that survives long after the organic elements have rotted away. The site at Cullen sits on the eastern bank of a stream, exactly the kind of low-lying, waterside location where these monuments are typically found. Most fulachtaí fia in Ireland date to the Bronze Age, broadly the period from around 2500 to 500 BC, though some have produced dates ranging earlier or later.

What makes the Cullen example quietly interesting is its scale. A spread of 22 by 14 metres represents a substantial accumulation of discarded burnt stone, suggesting repeated, perhaps sustained use of the site over a long period rather than a single occasion. The fact that it survives at all within cultivated land is itself notable; tillage has a tendency to disturb and erode such low earthworks over generations of ploughing.