Tang Dynasty China. 618-907 Kai Yuan Tong Bao. A scarcer large variant exceeding 26mm. Jade green and cobalt blue patina. The Tang Dynasty is one of China's most illustrious periods. After a few hundred years of disunity following the collapse of the Jin 晋 Dynasty, the Tang Dynasty inherited a unified kingdom from the short lived Sui 隋 Dynasty. However under the capable leadership of a few generations of Emperors such as Emperor Taizong and the Empress Wu Zetian, the Chinese experienced a period of cultural, technological and military strength unrivaled by preceding as well as most subsequent Dynasties. The Kai Yuan Tong Bao meant "circulating treasure from the inauguration of a new epoch". It was the first time Chinese coins adopted a titular inscription as opposed to a weight age equivalent that was the standard for the past thousand over years (ref: Ban Liang and Wu Zhu etc). The quality was of exceptional quality and became the defacto standard imitated by her neighbors both in the East (Japan, Korea) and the West (ergo Sogdian and central asian). The Tang Dynasty was also the first adopt the inscription Tong Bao 通寶 and Yuan Bao 元寶 which became the mainstream text of pretty much all cash coins across Asia up to the 20th century.