Tang Dynasty, Anonymous Middle Type, 718 - 732 ADAE Cash, 25mm, 4.23 gramsObverse: Kai Yuan Tong Bao.Reverse: Upwards crescent control mark above.Hartill14.4uThe Tang coinage marks great change in the history of Chinese coinage. Emperor Gao Zhu first introduced the Kai Yuan in 621 AD, and this coin type would remain the standard for 300 years. The earlier pieces are of the highest quality, with the calligraphy of the most elegant style. The series was anonymous, with the types only being categorized by quality of manufacture and style of calligraphy. Many of these coins bear a small crescent on the reverse in various locations. Legend has it that the empress Wende put her fingernail into a wax mould, creating the mark which was duplicated on the coins. Nice story, but undoubtedly these are mint control marks.