2, copper coins, also known as "copper coins." Copper coins mainly refer to non-porous copper coins in the late Qing Dynasty and the early Republic of China. China was the first country to use metal currency. Among the metal currencies, copper coins were the main ones in the past dynasties. Therefore, the ancient currency history of China is actually the history of copper coins. During the Yin and Zhou Dynasties, China used tooth shells as its currency, but because the real shells were not enough, they were replaced by imitation copper shells. Copper shell is the transitional form of metal currency. After Qin Shihuang unified China, he unified the monetary system. Scrap knives, cloth, shells and other coins, it is stipulated that only square hole coins with a square hole in the middle of the outer circle are used, which evolved from ring coins. The currency after the Qin dynasty was square hole money, but the name was different.