A ryō (両) was a gold piece in pre-Meiji Japan. It was worth about sixty monme of silver or four kan (4,000 coins) of copper (the exchange rate fluctuated). It was eventually replaced with a system based on the yen.
The ryō was originally a unit of weight from China, the tael. It came into use in Japan during the Kamakura period. By the Azuchi-Momoyama period it had become nearly uniform throughout Japan, about 4.4 monme as a unit of weight (about the same as 16.5 g). The Keichō koban, a gold piece, contained about one ryō of gold, so that koban carried a face value of one ryō. However, successive mintings of the koban had varying (usually diminishing) amounts of gold (debasement). As a result, the ryō as a unit of weight of gold and the ryō as the face value of the koban were no longer synonymous.
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