e did
not remain long in force, nor have there survived any coins, whether
of silver or of copper, certainly identifiable as antecedent to the
Wado era. It was in the year of the Empress Gemmyo's accession (708)
that deposits of copper were found in the Chichibu district of
Musashi province, and the event seemed sufficiently important to call
for a change of year-name to Wado (refined copper). Thenceforth,
coins of copper--or more correctly, bronze--were regularly minted and
gradually took the place of rice or cotton cloth as units of value.

It would seem that, from the close of the seventh century, a wave of
mining industry swept over Japan. Silver was procured from the
provinces of Iyo and Kii; copper from Inaba and Suo, and tin from
Ise, Tamba, and Iyo. All this happened between the years 690 and 708,
but the discovery of copper in the latter year in Chichibu was on
comparatively the largest scale, and may be said to have given the
first really substantial impetus to coining. For some unrecorded
reason silver pieces were struck first and were followed by copper a
few months later. Both were of precisely the same form--round with a
square hole in the middle to facilitate threading on a string--both
were of the same denomination (one won), and both bore the same
superscription (Wado Kaiho, or "opening treasure of refined copper"),
the shape, the denomination, and the legend being taken from a coin
of the Tang dynasty struck eighty-eight years previously. It was
ordered that in using these pieces silver should be paid in the case
of sums of or above four mon, and copper in the case of sums of or
below three won, the value of the silver coin being four times that
of the copper. But the silver tokens soon ceased to be current and
copper mainly occupied the field, a position which it held for 250
years, from 708 to 958. During that interval, twelve forms of sen*
were struck. They deteriorated steadily in quality, owing to growing
scarcity of the supply of copper; and, partly to compensate for the
increased cost of the metal, partly to minister to official greed,
the new issues were declared, on several occasions, to have a value
ten times as great as their immediate predecessors. Concerning that
value, the annals state that in 711 the purchasing power of the mon
(i.e., of the one-sen token) was sixty go of rice, and as the daily
ration for a full-grown man is five go, it follows that one sen
originally sufficed for twelv