The ban liang coin was first issued in the Qin dynasty during the reign of China’s first emperor, Qin Shi Huang, who unified China's politically warring states in 221 BC and their currencies in an effort to lay secure foundations for a new centralized state. The coin was round with a square hole in the middle, reflecting the traditional cosmology of East Asia in which the sky is round and the earth square. Thereafter, the shape of the ban liang coin became the standard form for other coins made across Korea, Japan and Vietnam, as well as in China in the following periods. The coin took its name from the two-character inscription, ban liang (半兩), in seal script. The liang is an ancient unit of weight consisting of 24 zhu (or su), each of which is equivalent to about the weight of 100 grains of black millet, approximately 0.65 grams, and, accordingly, a ban (“half”) liang consists of 12 zhu, or approximately 7.8 grams.