Kaiyuan Tongbao, Tang dynasty (AD 618-907). Copper. Diameter 23.89 mm. © Shanghai Museum

The Zhu Liang monetary system which had been used as the name and unit of the currency was abolished in the 4th year of Wude Period of the Tang dynasty (AD 621). The monetary system of Bao Wen began in practice, with Tong Bao, Zhong Bao used as names for the currency and Wen as the unit.
With the development of a commodity economy in the Tang dynasty, the demand for copper coins surged. But since the mid-Tang dynasty, copper coins became in increasingly short circulation on the market. In the 5th year of Huichang Period (845), Emperor Wuzong of the Tang dynasty implemented the law of ‘Buddha Abolishment’ to collect the bronze statues of Buddha and bronze wares all over the country to cast coins of Kaiyuan Tongbao. Because most of the coins of Kaiyuan Tongbao were minted with the names of prefectures, different from other Kaiyuan coins, they were thus called as Huichang Kaiyuan. In addition to the prefecture name Lan, there are three balls of clouds on the back of the coin, which is quite rare among Huichang Kaiyuan coins.