Kocho Junisen

kōchō jūnisen (皇朝十二銭) (aka jūnizeni) is a general term for 12 types of copper coins minted in Japan under the Ritsuryo system from 708 (Wadō 1st year) to 963 (Ōwa 3rd year). All of the included coins are circular in shape, have a square hole in the center, and were worth 1 mon.