Cash coins are a type of historical Chinese, Japanese, Korean, Ryukyuan, and Vietnamese coin design that was the main basic design for the Chinese cash, Japanese mon, Korean mun, Ryukyuan mon, and Vietnamese văn currencies. The cash coin became the main standard currency of China in 221 BC with the Ban Liang (半兩) and would produced until 1912 AD there with the (民國通寶), the last series of cash coins produced in the world were the French Indochinese Bảo Đại Thông Bảo (保大通寶) during the 1940s. Cash coins are round coins with a square centre hole. It is commonly believed that the early round coins of the Warring States period resembled the ancient jade circles (璧環) which symbolised the supposed round shape of the sky, while the centre hole in this analogy is said to represent the planet earth (