Captioned: "Workshop of caster during Bronze Age. The alloy, having been previously mixed, has been smelted in a furnace, an a workman is pouring it into a sand-mold. Another man is examine a sword-blade which has just been cast." Humans learned to smelt metals in prehistoric times, more than 8000 years ago. The discovery and use of metals, copper and bronze at first, then iron a few millennia later, had an enormous impact on human society. The impact was so pervasive that scholars traditionally divide ancient history into Stone Age, Bronze Age, and Iron Age. An ancient civilization is defined to be in the Bronze Age either by smelting its own copper and alloying with tin, arsenic, or other metals, or by trading for bronze from production areas elsewhere. "Primitive Man" by Louis Figuier, 1871.