A fulacht fiadh (Irish pronunciation: [ˈfˠʊl̪ˠəxt̪ˠ ˈfʲiːə]; Irish: fulacht fiadh or fulacht fian; plural: fulachtaí fia or, in older texts, fulachta fiadh) is a type of archaeological site found in Ireland. In Great Britain and the Isle of Man they are known as burnt mounds. They commonly survive as a low horseshoe-shaped mound of charcoal-enriched soil and heat shattered stone with a slight depression at its centre showing the position of the pit.
Radiocarbon dating indicates that the majority of fulachtaí fiadh were constructed during the mid to late Bronze Age (c.1500- c. 500 BC), though some Neolithic examples are known. However, some were still in use up to medieval times. Permanent structures are rarely found near to fulachtaí fiadh, but small hut sites are common and it is unknown whether early sites were built by permanent settlements or nomadic hunters.
Many commentators suggest that the Irish word "fulacht" denotes a pit used for cooking. "Fiadh" in Old Irish meant something like "wild", often relating to animals such as deer. However, all commentators acknowledge significant difficulties in deriving a genuine etymology for the word "fulacht". As some historical references clearly use the term "fulacht" to describe a cooking spit, a close reading of these accounts suggests that the term actually derives from a word meaning support and probably carries a deliberate reference to the Irish words for blood and meat.
Fulachtaí fiadh are usually found close to water sources, such as springs, rivers and streams, or waterlogged ground. They were also sited close to sources of suitable stone where it could be obtained close to the surface. They required a source of fuel, so would have been close to woodland. They would also have to be in proximity to whatever was being processed by boiling in the trough. Once these conditions were met a fulacht fiadh could be constructed. Once the use of a fulacht fiadh had ended it was common for people to continue to make use of the local landscape, therefore fulachtaí fiadh tend to be found in groups strung out along water courses.