Since then, and for more than three centuries, the furnaces have proliferated within the city walls (built in the mid-14th century), to over 50 units at the end of the 15th century. The production level was such that required an “Editto del Potestà” (Edict) to prohibit that the huge quantities of waste and processing residues were thrown in the adjacent Pesa River, so to avoid its stream to be diverted.