It measures roughly twenty metres north to south and eight metres east to west, rising no more than twenty centimetres above the surrounding land. That modest hump is, in fact, the accumulated debris of prehistoric cooking, and it has sat quietly in this field for perhaps three or four thousand years.

The mound is a fulacht fia, a type of site found in enormous numbers across Ireland, particularly in low-lying and waterlogged ground. The basic technology was straightforward: a trough, usually timber-lined or stone-lined, was filled with water, and stones were heated in a nearby fire before being dropped in to bring the water to a boil. Over repeated use, the spent and shattered stones were discarded to one side, gradually building up the characteristic horseshoe-shaped or oval mound of dark, heat-cracked material that survives today. The proximity of marshy ground at Rockspring is entirely typical; fulachta fiadh are almost always found near a reliable water source, and boggy or low-lying areas provided exactly that. The dark, burnt-looking composition of these mounds, a crumbly mix of charcoal, ash, and fire-shattered stone, is usually what distinguishes them in the field from ordinary earthworks.