Yuan Dynasty Coins and Japan — The Economic History of Medieval Japan Woven by Foreign Copper Coins

In the 13th century, the Yuan Dynasty, which ruled the vast territories of the Mongol Empire, introduced a revolutionary currency system to govern their expansive domain. From the time when the first emperor Kublai Khan established the country name as 'Yuan' in the 8th year of Zhiyuan (1271), they consistently promoted paper currency 'Jiaochao' as the main currency. Particularly in the 24th year of Zhiyuan (1287), they focused on maintaining the credibility of paper money by collecting old Jiaochao and issuing new currency 'Zhiyuan Tongxing Baoshao.' However, this paper-money-centric approach sometimes brought inconvenience in small transactions in rural areas and overseas trade. As a solution, the Yuan Dynasty also carried out the minting of copper coins as auxiliary currency or to facilitate smooth circulation. Major copper coins include Zhiyuan Tongbao, whose casting began in the 2nd year of Zhiyuan (1264), 'Zhida Tongbao' issued in the 1st year of Zhida (1308), and 'Dayuan Tongbao' minted in the 7th year of Yanyou (1320). These copper coins were manufactured at the Baoquan Bureau established in Dadu (present-day Beijing) and various local mints. Although the Yuan Dynasty relied domestically on paper currency, they continued to supply copper coins to meet the demands in trade with neighboring countries and in remote regions where paper money was not readily available. Despite the military conflicts during the Mongol invasions in the 11th year of Bun'ei (1274) and the 4th year of Kōan (1281), trade relations with Japan resumed underneath the surface in the ten years following these events. Merchants based in Hakata engaged secretly in trade with Yuan merchants, and Yuan copper coins were transported across the East China Sea to Japan along with goods such as raw silk, ceramics, and spices. Although these copper coins were an auxiliary element in the Yuan currency system, they profoundly impacted Japan's economy as the coins 'crossing the sea.' It marked an era when foreign coins began entering, contrasting with Japan's historical approach to domestic coinage as seen in the detailed explanations of Wado Kaichin.

Yuan Dynasty copper coins were created using traditional Chinese casting techniques. The major mint was Baoquan Bureau situated in Dadu (now Beijing), alongside local mints managed by administrative provinces. These mints utilized the 'sand-casting method,' a technique involving melting bronze composed mainly of copper with lead and tin, pouring it into sand molds. This method produced round copper coins with a square hole, approximately 23mm to 25mm in diameter and weighing about 3 to 4 grams. Inscriptions such as 'Zhiyuan Tongbao' and 'Dayuan Tongbao' were common, and various calligraphy styles were used. Besides reinforcing the Yuan Dynasty's currency circulation, these copper coins served as means of transaction in foreign trade. Main trading ports during the Yuan period included Quanzhou in Fujian province and Guangzhou in Guangdong province, from where many trading ships set sail. Especially, Quanzhou was described by Marco Polo as a 'center of world trade,' with merchants and goods from various countries gathering there. Even after the Mongol invasions, Japanese merchants continued trading across the East China Sea using Yuan trading ships or their own vessels from these ports. They brought Japanese sulfur, swords, and lacquerware to China and returned with Yuan silk, ceramics, medicinal materials, and copper coins. Though the sea route was dangerous, often threatened by storms, the vast profits from trade drove many merchants. Hakata, owing to its geographical advantage, became the major gateway for Yuan coins to land first, distributing from there across Kyushu and further into the Kinai region. At the time, voyages could take weeks to months one-way due to the navigation technology available, and despite the difficulties, the foreign copper coins successfully arrived in Japan. Today, when these Yuan coins appear in ancient coin auctions, the historical context is always discussed.

Yuan coins began to flow into Japan starting from the 1280s after the conclusion of the Mongol invasions. Northern Kyushu, particularly Hakata, became a primary hub for private trade with the Yuan, where Yuan coins first circulated. During this time, Japan had limited capability to mint its own coins and heavily depended on Chinese Song coins since the late Heian period. The addition of Yuan coins diversified Japan's currency economy. Copper coins such as Zhiyuan Tongbao and Dayuan Tongbao circulated alongside Song coins for a wide range of uses from small transactions to large-scale trade. Especially during the Nanbokuchō period (1336-1392), Japan was embroiled in intense conflict between the Muromachi shogunate and the Southern Court, leading to extreme societal confusion. Paradoxically, this political turmoil accelerated the development of Japan's money economy. The demand for goods due to warfare and the increased economic activity of the warrior class greatly raised the demand for currency. During this period, coupled with the decline of the Yuan and the rise of the Ming Dynasty amid China's political unrest, the inflow of Yuan coins into Japan further increased. Records from the Ōei period (1394-1428) show active circulation of Yuan coins in Japanese markets. However, the coexistence of various types of coins led to confusion over the quality and value of the coins. Frequent coin selection, known as 'Erizeni,' involved selecting good coins from the bad, sometimes prompting the shogunate to issue coin-selection laws to restrict certain coins or define exchange rates. The people, initially bewildered by foreign coins, soon adopted them for daily use due to their convenience. Yuan coins boosted product circulation and indirectly sustained economic growth during the medieval period. The distinction of counterfeits and processed items, which was a factor hindering circulation then as now, remains pertinent.

The influence of Yuan Dynasty coins on Japan's economy lingered prominently in subsequent currency history. After the Yuan Dynasty fell in the 28th year of Zhizheng (1368) and the Ming Dynasty was established, the source of copper coin supply to Japan shifted to the Ming Dynasty. From the mid-Muromachi period onward, Ming coins such as Yongle Tongbao and Hongwu Tongbao began to flow in large numbers, eventually replacing Yuan coins as the primary currency. However, Yuan coins did not entirely disappear. Historical records like the 'Tamoin Diary' compiled during the Eiroku period (1558-1570) indicate that Yuan coins were still circulating in the market, revealing their long lifespan. The Muromachi shogunate attempted to resolve coin-selection chaos by repeatedly issuing coin-selection laws. For instance, in the 18th year of Ōei (1411), they enacted a law banning the circulation of bad coins, targeting even Yuan coins for selection. Inferior quality Yuan coins were gradually eliminated from the market, yet high-quality ones continued to be used for a long time. The inflow of Yuan coins symbolizes a transitional period in Japan's monetary economy, shifting from the imperial Shinjūsen (Twelve Coins of the Imperial Court) minted domestically to an international currency system centered on Chinese coins. It was not only about the mere circulation of coins but also evidence of Japan's growing economic ties with the Chinese mainland, actively participating in global trade at the time. In the present, Yuan coins are excavated from archaeological sites like the Hakata ruins and Kōrokukan ruins in Fukuoka City, centered in northern Kyushu. These findings are valuable archaeological materials illustrating the active international exchange of the time, remaining indispensable in medieval Japanese economic history research. The Yuan coins that supported Japan's economy beyond the era of conflicts like the Mongol invasions continue to narrate their history quietly. As symbols of the era when foreign currency, different from the domestic coins like the detailed Keichō Koban, moved the economy, their value is immeasurable.