These accumulations of fire-cracked rock and dark, charcoal-rich soil are found in their thousands across the country, typically close to water, and are generally associated with the Bronze Age, though their precise function remains debated. Cooking is the most widely accepted explanation, with water heated by dropping fire-heated stones into wooden troughs, but other uses, from textile processing to communal bathing, have all been proposed.

The burnt mound at Johnstown in County Wicklow came to light during the construction of the Arklow bypass road scheme, when archaeologist Niall Gregory excavated the site under licence 97E0252. The dig uncovered two pits and three troughs, along with four distinct spreads of burnt material, the signature debris of repeated stone-boiling activity. One of the troughs retained evidence of two post-holes, suggesting some kind of timber structure had been associated with it, perhaps a frame to support a vessel or a simple shelter over the working area. Twelve worked flints were also recovered from the site, though their precise relationship to the burnt mound activity could not be established, as none came from a securely stratified context. Worked flint of this kind, stone shaped by deliberate knapping into tools or blades, is a common find across prehistoric sites in Ireland, but without a clear stratigraphic position the Johnstown pieces cannot be tied confidently to a specific period or activity.