The was a gold currency unit in the shakkanhō system in pre-Meiji Japan. It was eventually replaced with a system based on the yen. Origins 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 grams). During the Sengoku period, various local daimyō began to mint their own money. One of the best known and most prestigious of these private coins was the koshukin issued by the warlord Takeda Shingen, who had substantial gold deposits within his territories. The value of the koshukin was based on its weight, with one koshukin equal to one ryō of gold, and thus stamped with its weight (about 15 grams). During the Tenshō period (1573–1592), one ryō was equal to four koku of rice, or 1000 brass coins. Tokugawa period The Tokugawa shogunate attempted to create a central currency, based on gold, silver and copper units all exchangeable at fixed rates. Oblong gold coins, called koban, were minted with one koban containing about one ryō of gold, so that koban carried a face value of one ryō. The official rate was set in 1609 at one ryō equal to 50 monme (approx 187 grams) of silver, or 4000 brass coins. However, in reality the relative values between gold, silver and brass currencies fluctuated on an almost daily basis throughout the Edo period. In 1695 the government decided to increase the amount of metal money in circulation by 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. The Keichō koban issued after the monetary reform of May 1601 offered approximately 17.9 grams gold with fineness of 84–87%. The Genroku koban issued in 1695 still weighed around 17.9 grams; however its gold content was reduced to 57%. The Hōei koban of 1706 returned to the original fineness; however, the size was much reduced and it had little more than half the metal value of the Keichō koban. In 1700 the official exchange rate was adjusted to 1 ryō equal to 60 monme silver (225 grams) or 4000 brass coins. Tokugawa Yoshimune further conducted a reform to stimulate the economy and raise prices