Kocho Junisen
kōchō jūnisen is a general term for 12 types of copper coins minted in Japan under the Ritsuryo system from 708 to 963. All of the included coins are circular in shape, have a square hole in the center, and were worth 1 mon.
History
Japan's first formal currency system was the Kōchōsen. It was exemplified by the adoption of Japan's first official coin type, the Wadōkaichin. It was first minted in 708 CE on order of Empress Genmei, Japan's 43rd Imperial ruler. "Wadōkaichin" is the reading of the four characters printed on the coin, and is thought to be composed of the era name Wadō, which could alternatively mean "happiness", and "Kaichin", thought to be related to "Currency".The Kōchōsen Japanese system of coinage became strongly debased, with its metallic content and value decreasing. By the middle of the 9th century, the value of a coin in rice had fallen to 1/150th of its value of the early 8th century. By the end of the 10th century, compounded with weaknesses in the political system, this led to the abandonment of the national currency, with the return to rice as a currency medium. The last official Japanese coin emission occurred in 958, with very low quality coins called Kengen Taihō, which soon fell into disuse.