Bronze is an alloy composed of copper and tin, though sometimes other substances, such as arsenic, are substituted for the tin. Bronze is harder than pure copper, making it a more durable material for weapons, hardware and sculpture.
In addition to having increased durability, bronze has a lower melting point than copper, making it easier for smiths to melt and shape. At first, ancient smiths used arsenic to make bronze, however, bronze made with tin became the dominant form of the metal by the end of the third millennium B.C., due to its increased strength. Also, as arsenic is poisonous, over time its fumes proved debilitating, which made it less attractive as a metallurgical component.