At Rathkelly in County Mayo, one such mound survives, a low crescent-shaped heap of fire-cracked stone and charcoal-dark earth that would be easy to walk past without a second thought. Yet these modest features, found typically beside streams or boggy ground, represent repeated, deliberate activity stretching back perhaps three and a half thousand years.

The standard interpretation is that burnt mounds, known in Irish archaeological literature as fulachtaí fia, were used for heating water. Stones would be fired in a hearth, then dropped into a water-filled trough, bringing the contents rapidly to a boil. What the heated water was used for remains genuinely debated: cooking, textile processing, bathing, and brewing have all been proposed, and the evidence does not firmly exclude any of them. What is consistent is the sheer repetition implied by the accumulated debris. A mound like the one at Rathkelly is essentially a spoil heap, the discarded stone that cracked and became useless after each heating cycle, piled up over many uses across what may have been generations. The presence of such a monument in this part of Mayo speaks to a settled or at least regularly revisited Bronze Age presence in the landscape, people who returned to the same spot, built their fires, and went about whatever task the heated water served.