木簡に見る和銅年間以前の銀と銀銭の計量・計数単位

抄録

Recently an excavation at the site of Fujiwara Capital, Nara unearthed a wooden tablet dating from the Taiho era (701-703) containing the phrase "5 ryo and 2 mon of silver 銀五両二文". Ryo is a weight unit and the mon is a unit of currency. Therefore, this tablet substantiates the author's hypothesis that "plain silver coins" were Japan's earliest money and that they had fixed metal value. He also checked other wooden tablets that might relate to silver or silver coins and reached the following conclusions. 1. There were silver coins weighing one bu 分 since before the Fuhon and Wadokaiho coins. Bu is a weight unit introduced from China. These coins were counted by units of bu or mon 文 and four pieces made up one ryo 両. Bu stressed weight while mon was a coin unit. 2. Another unit seen on wooden tablets is hyo or hakari 秤 (weighing), which was used only for silver so far as we know. An unfamiliar unit han 楓, appears often used together with hyo. This usage strongly suggests that the term han itself designated the applied material, which was the same or similar to silver. On the uses of han and hyo, they are not seen in relation to high and low unit ranks. Han is always used with an integral number but hyo often has a half fraction. Therefore han was a unit to count plain silver coins like mon. and the hyo was a unit of the same value but used in the case of weighing like bu. 3. The creation of special Japanese unit names possibly resulted from the order of the 12^th year of Emperor Tenmu, which prohibited silver coins and allowed its use as metal silver alone. People had to refrain from using currency unit names in order to show that they were obeying the order. The distinction between counting and weighing units must have been caused by the emergence of altered coins reduced in weight, which is inevitable for coins of fixed metal value. 4. Silver plain coins were used frequently enough to give rise to Japanese proper unit names. Some wooden tablets record that they were used to purchase high-quality cloth ra or pay "plough costs". Another tablet reveals that silver coins were sent from provinces far from the capital, such as Wakasa, Iki, and Shima. 5. By the Taiho era, silver coins were fully revived and counted by mon. the normal name of a coin unit, at the Central Ministry. The existence of plain silver coins was the basis of wily policy to replace them with silver coins of Wado-kaiho and then by copper coins of the same name all at the same exchange value.