That, in a way, is what makes it interesting. Somewhere beneath ordinary pasture on the south-eastern bank of a small stream in County Mayo lies the remnant of a burnt mound, a type of prehistoric site so commonplace across Ireland that archaeologists sometimes call them fulacht fiadh. The name refers to a mound of fire-cracked stone and charcoal-blackened soil, the accumulated debris of repeated heating: stones were typically fired and dropped into water-filled troughs to bring the liquid rapidly to the boil. What they were used for, cooking or bathing or some industrial process, remains genuinely debated. At Cloonbullig, even the mound itself has disappeared; the only trace is what lies underneath the grass.

When the site was inspected in 1998, a layer of black, charcoal-rich soil packed with shattered stone was visible in cross-section along the stream bank, exposed where the bank had been cut away to give farm livestock access to the water. The layer measured around 1.5 metres in length and between 0.15 and 0.2 metres in depth at the cut, though it was not possible to determine how far it extended beyond that point. The shattered stone is characteristic of the process itself; repeated thermal shock causes rock to fracture, and over time the discarded fragments accumulate into the distinctive mounded shape that gives these sites their name. Here, no such mound survives above ground, leaving only this thin, dark seam as evidence that the place was once, at some prehistoric moment, a site of sustained activity.