Wadōkaichin influenced by Kaiyuan Tongbao
Description
The wadōkaichin was first produced following the discovery of large copper deposits in Japan during the early 8th century.The coins, which are round with a square hole in the center, remained in circulation until 958 CE.  These were the first of a series of coins collectively called jūnizeni or kōchō jūnisen (皇朝十二銭).This coinage was inspired by the Chinese Tang dynasty coinage (唐銭) named Kaigen Tsūhō (Chinese: 開元通宝, Kāiyuán tōngbǎo), first minted in Chang'an in 621 CE. The wadōkaichin had the same specifications as the Chinese coin, with a diameter of 2.4 cm and a weight of 3.75 g.