Japan used a standard currency of “Mon” coins from the “Muromachi” period in 1336, until the early “Meiji” period in 1870. These periods are named after the shogun (emperor, or ruling family) of the time. These were cast round coins with a square hole, not dissimilar from Chinese “Cash” coins, such as this Northern Song 2 Cash coin.

From 1636, the Tokugawa, or “Edo” shogunate standardised on “Kan’ei Tsuuhou” coins, which had the following characters:

　寛
寶　通
　永

This translates to “Currency of Kan’ē Period.”, the era name of the time.

In the 1760s, the Tokugawa, or “Edo” shogunate, first commissioned the first 4 mon coin. These were slightly larger than the 1 Mon coin, but worth four times as much, so were very cost effective to produce. These were visually distinctive from 1 Mon coins as they had 21 “waves” on the reverse:

The following year, a simpler “11 wave” design was used, which continued for all subsequent 4 mon coins:

These were popular and Luke Roberts has illustrating some the variation in batches from 1768 – through to 1866. In 1868, a young Emperor Meiji took the throne and began what is known as the Meiji Restoration. The next twenty years saw huge changes in Japan, including industrialisation and adoption of many western ideas. In terms of money, this meant changing the currency from cast Mon coins, to modern minted coins; the Yen Japan still uses today.