The Mongol Invasions and the Sword Revolution

The Mongol Invasions — An Unprecedented Threat

In the 10th month of Bun'ei 11 (1274), a massive combined Mongol and Goryeo fleet landed on the shores of Hakata Bay in northern Kyushu. The Bun'ei Campaign was the first full-scale invasion of Japan by a foreign military, and it presented Japan's samurai with shocking combat experience. The following campaign, the Kōan Campaign of Kōan 4 (1281), saw an even larger expeditionary force attack. In both campaigns, however, the Yuan forces were struck by storms at sea, known as kamikaze ("divine wind"), and withdrew after suffering heavy losses.

The tactics of the Mongol forces were unlike anything the samurai of Japan had experienced. Traditional Japanese battle had once been said to be based on one-on-one duels, in which warriors announced their names with the call "Yā yā, ware koso wa" before competing in individual prowess. The Mongol forces, by contrast, massed in dense formations and attacked with organized group tactics that combined bows and arrows, long-hafted weapons, and gunpowder weapons. The tetsuhō (exploding bombs), in particular, produced explosive noise and flames, and their psychological effect was strong, panicking samurai and horses alike.

The Impact of Combat Experience on Sword Design

In the late Kamakura period, the upheavals of the two Mongol invasions and the collapse of the political order further spurred sword-making.

Tachi of this period were a bolder version of the form seen in the mid-Kamakura period. They had wider mihaba (body width), a smaller difference between the moto-haba and saki-haba (width at the base and at the tip), and a growing number had longer kissaki. Overall, however, the kasane was thin. These tachi served as a bridge to the ōdachi of the later Nanboku-chō period.

Technical Innovation Among Swordsmiths

The shape of the sori was also reconsidered. When cavalry charges and close combat on the battlefield were taken into account, an appropriate sori improved cutting efficiency, but excessive curvature made the blade harder to handle. Tachi of the late Kamakura period following the Mongol invasions tended to shift from koshi-zori toward torii-zori and naka-zori, which curve evenly along the entire length rather than concentrating curvature in the lower part of the blade. This reflected efforts to adapt to varied combat situations.

In the Osafune school of Bizen Province, master smiths such as Nagamitsu, Kagemitsu, and Kanemitsu left works that record the changes around the time of the Mongol invasions. In particular, the distinctive hamon known as kataochi-gunome, which Kagemitsu originated, reflects the vibrant atmosphere of technical innovation after the Mongol invasions.

The Kamikaze Legend and the Samurai Spirit

The storms that contributed to the final repulse of the invaders in the two Mongol invasions came to be called kamikaze ("divine wind"), and they spread the belief that the gods and buddhas protected Japan. This experience was deeply etched into the Japanese psyche and further reinforced the belief that the sword was a sacred weapon blessed by the gods and buddhas. The custom of dedicating swords to shrines and temples also became even more widespread after this period.

The Kamakura shogunate mobilized enormous costs and manpower to defend against the Mongol invasions, but it was unable to grant adequate rewards. As a result, economic exhaustion among the gokenin (shogunal vassals) and discontent with the shogunate built up. This contradiction became one of the remote causes of the later fall of the Kamakura shogunate (1333) and the Nanboku-chō turmoil.

Significance for Appreciation

Tachi from around the time of the Mongol invasions, particularly works from the late Kamakura period, hold special meaning for collectors. They are living witnesses to history: Japanese swords that changed form to meet the demands of actual battlefields, rather than existing only as pure works of art. Their imposing form, with broad mihaba and extended kissaki, carries the memory of the tension and ingenuity of the samurai who confronted the Mongol forces.