 During the Western Han dynasty (206 BC – 9 AD), the Wu Zhu bronze coins became the main currency in circulation, while hoof-shaped gold ingot known as "Horse Hoof Gold" () served as an adjunct currency for high-value transactions.During the Tang Dynasty, a standard bi-metallic system of silver and copper coinage was codified with 10 silver coins equal to 1,000 copper cash coins.Paper money and bonds started to be used in China in the 9th century.