Paper money was invented in China in the 9th century, but the base unit of currency remained the copper coin. The use of shell money is attested to in the Chinese writing system. The extent of the circulation of shell money is unknown, and barter trade may have been common. However, copies of cowry shells made out of bone, wood, stone, lead and copper were common enough to presume that they were used in trade. Chinese shell money, 16-8th century BCE. The Chinese may have invented the first metal coins, coins found in Anyang date to before 900 BC.
Bronze became the universal currency during the succeeding Zhou Dynasty. Ban Liang” based on the coins previously used by Qin. All other forms of local currency were abolished. The coins were round with a square hole in the middle which was the common design for most Chinese copper coins until the 20th century. China again reunited the currency system displacing coinages from ten or so independent states. Among pre-Song coins, the northern states tended to prefer copper coins. The southern states tended to use lead or iron coins with Sichuan with its own heavy iron coins which continued to circulate for a short period into the Song dynasty.