Introduction to unified coinage: To unify currency, Qin Shihuang ordered the state to unify coinage, severely punish private coinage, and put the manufacturing power of currency in the hands of the state. At the same time, he also unified the two popular currencies, namely gold coins for upper coins and copper coins for lower coins. The unit of gold was changed to "yi", and one yi was equal to twenty taels. Copper coins are in units of "half liang" and are shaped like round square holes, commonly known as "Qin Banliang".