Imagine that you are on a battlefield somewhere in the Middle East at the beginning of the Bronze Age. You advance with your copper sword and engage a foe armed with a bronze sword (a copper-tin alloy). He swings, you parry and your sword bends. Hopefully, you have time to retreat and bend your sword straight before you are slain. Whether such a scenario would have happened is debatable. The copper swords would have likely accidentally contained arsenic, which make them harder. Indubitably, bronze swords could keep a sharper edge. In fact, some swords made in China as early as the Warring States period (475–221 B.C.) were engineered to have a high tin content (17–21% tin) along the edge, which makes it harder and better at holding an edge but more brittle, while the center of the sword has a lower tin content (10%) and is softer but more ductile.