Banknotes first appeared in the Song Dynasty. Jiaozi is the earliest banknote in China and the earliest banknote in use in the world. During the Northern Song Dynasty, buying a piece of silk with copper coins required hundreds of kilograms of copper coins, which was very inconvenient to circulate. So merchants planned to issue a banknote named Jiaozi, and 30 copper coins would be deducted for each banknote during exchange.