These low, kidney-shaped mounds of fire-cracked stone and dark, charred soil are the remains of a cooking method used predominantly during the Bronze Age, roughly between 2000 and 500 BC. The typical process involved heating stones in a fire, dropping them into a water-filled trough to bring it rapidly to the boil, and then discarding the spent, shattered stones in a heap nearby. Over generations, those heaps became the mounds that survive today, sometimes barely distinguishable from a natural rise in a boggy field.

Burnt mounds, known in Irish archaeology by the somewhat prosaic label fulacht fiadh, are found in their thousands across Ireland, and Mayo has a considerable share of them. They tend to cluster near water sources, which makes practical sense given their dependence on a reliable supply. Whether the Aille mound sits close to a stream or a marshy hollow in the way that so many of its counterparts do is not recorded here, but the pattern is consistent enough to be worth bearing in mind. Beyond cooking, some researchers have proposed that these sites were used for bathing, textile processing, or brewing, though the heating of water remains the one function the archaeology consistently supports.