Standardized money was introduced in ancient China during the Qin Dynasty from 221-206 BC. Cast bronze coins with a square hole in the center became the dominant form of currency used throughout China. This coin design continued as the classical shape for Chinese currency for many dynasties until the Qing Dynasty from 1644-1911, although different monetary systems were also used. Some early forms of money in China included knife money, spade-shaped coins, and zhi coins during the Tang Dynasty, and later the first banknotes emerged in China.