Kan'ei Tsūhō — "Japan's Longest-Lived Coin" in Circulation for 230 Years

The reign of the third shogun Tokugawa Iemitsu (in office 1623–1651) is known as the period of establishment for the Edo shogunate system. The institutionalization of the sankin-kōtai (attendance by alternate residence) system in Kan'ei 12 (1635), the completion of the national isolation policy in Kan'ei 16 (1639), and the commencement of Kan'ei Tsūhō minting in Kan'ei 13 (1636) were all interconnected measures deepening centralization.

Before coin unification in Japan, there was a mixture of imported coins mainly from China, such as Eiraku Tsūhō, Hongwu Tsūhō, Xuande Tsūhō, and locally privately minted inferior "private cast coins" (shichū sen). Import of foreign coins was frequently disrupted, causing unstable supply, while private cast coins varied greatly in quality and were unreliable. In everyday transactions among commoners, "eri zeni" — the habit of picking good quality coins — was rampant, causing friction in commercial transactions.

Responding to Iemitsu's directive, the elder statesmen of the shogunate decided on the policy of mass supplying domestically minted coins. Mito domain, under the lordship of Tokugawa Yorifusa (ancestor of Tokugawa Nariaki), was selected as the first mint location due to its prior technical achievements, with the first Kan'ei Tsūhō minted in Mito in Kan'ei 13 (1636).

The surface of Kan'ei Tsūhō bore the four characters "寛永通宝" in seal script and had a square central hole called "sen" designed to string together for portage. By adopting the same hole coin format as imported coins, it retained practicality by accommodating existing customs for carrying and storing coins. The initial goal was to completely replace imported coins and privately minted coins, thus starting a massive minting effort.

After the start of minting in Mito, the shogunate expanded production by establishing and permitting mints across various regions. Mint locations gradually expanded to Edo (Honjo, Fukagawa), Kyoto (Fushimi), Omi (Sakamoto), Mutsu (Sendai), and Nagasaki, among others. Sendai domain (Date family) and Nagasaki became major production sites from early on.

Differences in local copper materials, minting techniques, and supervisory systems in these mints led to variations in typography, weight, and copper color. Although the shogunate stipulated standards (diameter and weight criteria), precise management did not extend to remote areas, giving rise to "production site variations." This is the cultural background for how they are classified in the modern collection world as "○○ coins" and "○○ mint."

Iron Kan'ei Tsūhō ("tessen") was also minted at different times and regions. Iron coins were used as substitute material during copper shortages, but they are more prone to corrosion and fewer exist today. Brass Kan'ei Tsūhō (an alloy of copper and zinc) have also been confirmed, making material diversity another classification point in collections.

There are abundant typography variations, with categories like "Standard Text (standard kaisho)," "Old Kan'ei (unique early typography)," and "New Kan'ei (well-formed later typography)" used in the detailed types of Kan'ei Tsūhō. Old Kan'ei (early minting from Kan'ei 13–17 = 1636–1640) is given special treatment in the collection world due to its first historical value.

The early Mito-produced Kan'ei Tsūhō has a high degree of typographic uniqueness, distinctly differing in penmanship from the later increased Edo and Kyoto productions, making it essential for collectors to start with provenance distinctions. The study of typographic transitions across production sites from early Mito coins is considered the standard path for studying Kan'ei Tsūhō.

In the Edo period, Kan'ei Tsūhō was the medium for all daily transactions in the common economy. One mon was the smallest unit, a block of tofu cost 4–8 mon, kaike soba cost 16 mon, and a carpenter's daily wage was 200–300 mon (in the Genroku period), making Kan'ei Tsūhō a practical presence similar to today's 100 yen coin.

Edo's "botefuri" — itinerant peddlers carrying goods on balance poles — traded items like vegetables, fish, tofu, and oil almost entirely in Kan'ei Tsūhō. Tenement residents carried 10 to 100 mon worth of Kan'ei Tsūhō in their wallets (drawstring purses) as daily living expenses. In funerals, placing "six mon coins" in the coffin as fare for the River Sanzu crossing was customary, with six Kan'ei Tsūhō serving this purpose (this is the Edo period version of the Takeda Shingen flag symbol "six mon coins").

Economically, the Edo Three Currency System had gold coins (kobans, ichibukin) for "large transactions and hoarding," silver coins (chogin, ichibugin) for "medium commercial transactions," and coin currency (Kan'ei Tsūhō) for "daily small transactions," with Kan'ei Tsūhō being the lowest but most frequently traded, acting as the "circulatory system" of society.

Recreational culture too was deeply rooted in Kan'ei Tsūhō. Gambling, entertainments, and buying ukiyo-e prints — all were done with Kan'ei Tsūhō, financially supporting the common culture of Edo. Long after its stop in circulation post-Meiji, it slept as "old coins" in the drawers of people.

In mid-Edo, the upgraded version of Kan'ei Tsūhō, "four mon sen" appeared. Its official name was "tōshi sen," valued at 4 mon per piece. It was a larger copper coin equivalent to four Kan'ei Tsūhō (one mon coins), with a diameter of about 34mm and weight of about 6.8g, larger than one mon coins. The "wave coin" (namisen), with ripples carved on the reverse, is a representative design.

The first issuance of four mon coin is said to be Kanpō 3 (1743) (some say there were prototypes in the Genroku era). The "big coin worth four pieces combined" improved transactional efficiency, with demand expanding particularly along with late Edo commercial development. With both one mon and four mon coins coexisting in the market, a situation arose where "even the same 'Kan'ei Tsūhō' differs in size," requiring commoners to have intuitive knowledge of coin differences they were familiar with.

Iron four mon coins ("iron four mon sen") were also minted mainly during the Bunka period (1804–1818). It was a measure for copper shortages, but iron deteriorates quickly, making well-preserved iron four mon coins far fewer than copper counterparts.

In Meiji 2 (1869), the new government stopped minting new Kan'ei Tsūhō coins. However, they continued to circulate until the cessation order of Meiji 9 (1876). The circulation over 230 years holds the record as the longest for a single currency in Japan. Along with the discontinuation of Tenpō Tsūhō in the same year of Meiji 9, the Edo coin system fully closed its historical chapter. Modern-day surviving Kan'ei Tsūhō, with its massive mintage, is easy to obtain, though differences in condition, provenance, and types create an infinite variety, marking the entrance to the profound world of old coin collection.