These features, found in their thousands across Ireland, are among the most common prehistoric monuments in the country, yet they remain genuinely mysterious. The name translates loosely as "cooking place of the Fianna," though who used them and for what precise purpose has been debated for generations. The most widely accepted theory holds that water was heated by dropping fire-heated stones into a trough, and the characteristic horseshoe-shaped mounds of shattered, burnt stone that survive are the accumulated debris of that repeated process.

The Mossgrove example followed the typical pattern: a stream nearby to supply water, level ground for working, and a mound of burnt material built up over what may have been many episodes of use spanning years or centuries. The date of its levelling, 1976, places it in a period before Irish planning law offered much practical protection to unexcavated archaeological sites in agricultural settings, and it was not uncommon for fulachta fiadh to be cleared away during land improvement works without any excavation taking place. Whatever the mound contained, including any remnants of a trough, associated features, or organic material that might have helped date its use, was lost at that point. What remains is the record of its existence and its location beside the stream that once gave it meaning.