The Mysterious Burnt Mounds of the British Isles

Photo: David HawgoodFulacht fiadh at Irish National Heritage Park
They cover Britain and Ireland (6,000 in Ireland alone), and although people have been living around them since the Bronze Age, no one can say for certain what they were used for. The fulacht fiadh (pl. fulachtai fiadh), or 'Burnt Mounds' as they're known in the UK, are rectangular basins anywhere from a meter to two meters wide, about half a meter deep, and surrounded by horseshoe-shaped mounds composed of charcoal, soil and heat-split rocks.
It's the surrounding mound which gives archaeologists one of their main clues as to the troughs' purpose. Almost all believe they were used for boiling water – the other big clue being the availability of water at the sites, which are usually found in wet, boggy areas or where the troughs are fed by streams. The rocks used to construct the troughs are sandstone or limestone, often not found nearby, and which therefore must have been deliberately brought to the sites for that specific use.
Photo: Graham HornThe type of landscape where fulachtai fiadh are normally found, wet with surrounding growth used for fire fuel
Although archaeologists agree on the water-boiling aspects of the fulachtai fiadh, there is some controversy over what the water was then used for. The word 'fulacht' means 'cavity' in Gaelic, and was historically used to refer to places where food, in particular meat, was cooked ('fiadh' refers to wild animals such as deer). However this does not mean the fulacht fiadh troughs were necessarily giant stewpots.
Others have put forward the theory that the troughs may have been used for dyeing textiles, bathing (in the case of the larger ones), or even brewing beer. In 2007 a couple of enterprising archaeologists were able to produce a drinkable light ale from a fulacht fiadh, confirming their suspicion that the love of a good brew was behind the mysterious trough sites. To further support their argument they pointed to the grinding stones found at many fulacht fiadh sites and even, in one instance, traces of grain and wheat.
Photo: goforchrisThe remains of a burnt mound in Orkney, UK
They were built mostly during the mid-Bronze Age (c. 1500 - c. 500 BC) and occasionally even earlier, but we may never be completely certain of the purpose or purposes of the fulachtai fiadh. Whatever it was, the sheer number and distribution of these trough sites suggest that whatever they did, they did it well.