They appear, typically, as low spreads of fire-cracked stone and blackened earth, and for decades their purpose was debated. The site at Camlin in County Tipperary adds a particular twist to that debate, because what was uncovered here suggests not a straightforward heating system but something more carefully engineered, concerned less with brute heat than with the conservation and cycling of water.

When excavators first cleaned back the deposit, the burnt mound material, that characteristic dark spread of heat-shattered stone, turned out to have been smeared across the top of an earlier enclosure ditch fill, and was itself cut by the ditch, placing the sequence in an instructive stratigraphic relationship. Beneath it lay two large troughs. The first was rectangular and apparently wood-lined; it connected via a raised saddle to a second, oval trough, which had a drain running out to the west. The arrangement mirrors a known filtering technique: sediment would settle in the first trough, and cleaner water would spill over the saddle into the second. What makes Camlin unusual is that no incoming water channel was identified. The working interpretation is that water was heated in the rectangular trough by dropping in hot stones, a standard Bronze Age method, and as the volume expanded with the heat, water overflowed into the oval trough already partially warmed, where it could be brought rapidly to a full boil. The system, in other words, may have been designed to maximise efficiency by reusing rather than continually replenishing water. A scattering of stakeholes close to the troughs may relate to some structure built over or around them. Roughly forty metres to the north, testing recovered a copper alloy palstave axe, a type of flat or flanged bronze axe characteristic of the Late Bronze Age, buried deliberately in the ground. Its presence confirms sustained activity in the area during that period. The axe was sent to conservator Susannah Kelly for initial cleaning and conservation.