(2) Qin and Han Dynasties: it is stipulated that the round square hole money is the currency that passes through the whole country. In the Han dynasty, gold coins and copper coins were the main currencies. The weight of copper coins in the Han dynasty changed several times, and it was not until Emperor Wu of the Han Dynasty cast five baht that it stabilized.
(3) The Three Kingdoms: At that time, money was reduced, and cloth and grain became the main means of circulation. Cao Wei once abolished copper coins in the form of decrees and used physical transactions, and will abolish them in the future.
(4) Sui and Tang Dynasties: Five baht is still cast, and it is forbidden to use old coins of different sizes from the previous generation, which is conducive to the development of trade. In the early Tang Dynasty, when the currency system was reformed, Tang Gaozu ordered "abolishing five baht and using Kaiyuan Bao Tong instead". The newly minted "Kaiyuan Bao Tong" became the common currency of the Tang Dynasty, and later it was widely circulated. It is a model of all currencies in later dynasties. The establishment of counter shops specializing in currency deposits and loans is the earliest prototype of banks in China, which is six or seven hundred years earlier than financial institutions in Europe and the Mediterranean.
(5) Song and Yuan Dynasties: During the Northern Song Dynasty, the world's earliest paper money "Jiaozi" appeared in Sichuan. The development from metal currency to paper money is the inevitable result of social and economic development. The popularity of paper money reduces the burden of merchants carrying metal money, which is conducive to commodity exchange and reflects the high development of commerce.
(6) Ming and Qing Dynasties: In the early Ming Dynasty, the main currency was paper money, and the auxiliary currency was copper money. People were forbidden to use gold and silver for trading. By the middle and late Ming Dynasty, silver had become the main currency in general circulation.