Kai Yuan Tong Bao (618-907 AD)
Kai Yuan Tong Bao (Chinese: 開元通寶; pinyin: kāiyuán tōng bǎo; literally: "The Inaugural Currency") were the main coin issued by the Tang. It was cast for most of the dynasty, a period of nearly 300 years. It was first issued by the Emperor Gao Zu in the autumn of the 4th year of the Wu De period (August 621). Its diameter was to be 8 fen. The weight was set at 2.4 zhu, ten to the liang. 1,000 coins weighed 6 jin 4 liang. The legend was written by the famous calligrapher Ouyang Xun in a much admired mixture of the Bafen and Li (official or clerkly) styles of writing. This is the first to include the phrase tong bao, used on many subsequent coins. The inscription was used by other regimes in later periods; such coins can be distinguished from Tang coins by their workmanship. Minting and copper extraction were centrally controlled, and private casting was punishable by death.