The blast furnaces and forges ran on charcoal. The woods were the main source of this natural fuel, produced by colliers, professionals who specialised in charcoal burning.
Known in local dialect as the poiatt or puiat, the charcoal pile was a heap of wood to be turned into charcoal. The wood had to be stacked and burned with great precision in a level clearing, where the charcoal was produced for several decades or even centuries. This ongoing activity has led to the accumulation of layers of charcoal residue, making it possible to identify traces of a number of charcoal piles in the wooded areas.