The Mongol Invasions (1274 and 1281) and Japanese Swords: How Battle with Mongol Forces Shaped Kamakura-Period Blade Making

What is the Genkō Invasions? — Two Invasions by Foreign Armies

In 1274 (Bunei 11) and 1281 (Kōan 4), a coalition army of the Mongol Empire (Yuan) and Goryeo landed in northern Kyushu. These two invasions, called the "Bunei Invasion" and the "Kōan Invasion," were the largest-scale foreign military threats in Japanese history, delivering a profound shock to the Kamakura shogunate and samurai society.

The Genkō Invasions are commonly known as events where the invading army withdrew due to typhoons (the "divine wind"), but the experiences of close-quarters combat and archery during several days of actual fighting certainly brought about changes in the combat perspective and weapon philosophy of Japanese samurai society.

The Mongol Army's Tactics — The "Alien Warfare" Japanese Samurai Confronted

Combat among samurai during the Kamakura period was fundamentally based on cavalry archery with the bow as the primary weapon, combined with one-on-one tachi duals initiated by formal declarations of name. The tactics of the Mongol army, by contrast, were fundamentally different.

Group Formations (Dense Array Tactics) The Mongol army employed densely packed infantry formations that moved in unison at the sound of drums (taiko) and metal gongs (kanera). This emphasis on group coordination over individual prowess created confusion among Japanese samurai, who expected one-on-one duels.

Gunpowder Weapons (tetsuhau) Records indicate the use of explosive shells called "tetsuhau" (iron cannons). The blast and flash startled horses, rendering samurai cavalry charges ineffective. This was the first gunpowder weapon Japanese samurai had ever encountered, and its psychological impact was incalculable.

Poisoned Arrows and Barrage Fire Mongol bows were shorter than Japanese bows with shorter range, but excelled in area-saturation fire from massed formations. Records also document the use of poisoned arrows (Mongol arrows), and some samurai who were struck could not heal from their wounds.

Direct Impact on Japanese Swords — Evidence from Historical Records and Archaeology

The Problem of Cutting Power — Mongol Armor and Japanese Swords

Multiple historical records from the Bunei Invasion document Japanese samurai stating that "when we cut Mongol soldiers with tachi, they did not cut" (as in the *Hachimanno Mongol Record*, etc.). This can be attributed to several factors.

Heavily Armored Mongol Troops Mongol infantrymen wore armor such as "fukiate" (breastplates) or chain mail-type protection, which were smaller than the armor that Japanese samurai expected but were designed to resist thrusting more effectively than cutting. The fact that thrusting rather than cutting was required may have influenced later changes in sword form.

Blade Damage Records also survive of swords breaking and edges chipping after fierce fighting with the Mongols. Some scholars argue this prompted later strengthening of the blade through increased thickness (kasane) and weight.

Changes in Sword Form After the Genkō Invasions — Evidence from Archaeology and Kissaki Records

After the Genkō Invasions (Bunei and Kōan invasions: 1274–1281), swords from the late Kamakura period (late 13th to early 14th century) show the following changes.

Trend Toward Larger Kissaki A shift is observed from the typical "inokubi kissaki" (boar-neck point) of the pre-Genkō period to larger points. Some researchers interpret this increase in kissaki size as an adaptation to the Mongols' close-order group combat, as larger points improved thrusting ability.

Increase in Kasane A tendency toward greater thickness (kasane) in the blade is visible. In the Mongol army's close-quarters group warfare, repeated contact between swords and shields or armor caused chipping and breaking. This experience likely elevated demand for durability, influencing swords to become thicker and heavier.

Acceleration of Bizen and Soshu School Fusion From the late Kamakura period through the Nanbokuchō period, the "vigorous hamon with powerful nie" represented by Masamune (Soshu School) became fashionable. This trend aligns with the historical context in which the impact of the Genkō Invasions heightened interest in "practical combat strength."

The "Genkō Sword" Legend — Reality and Mythologization

Numerous swords and anecdotes attributed to the Genkō Invasions have been created by later generations. However, most exist only in the realm of legend.

Collection of "Mongol Swords" Some weapons and armor left behind by the Mongol army were carried away by samurai and temples as war trophies. Records document an influx of Mongol-made blades (scimitars and saber-type weapons) into Japan, where they were treasured as "foreign swords." Some of these are said to remain in museums and temples today, though few blades can be definitively identified as Genkō Invasion-related.

Takesaki Suenaga's Valor and Swords The "Mōkoshuurai Ekotoba" (Scroll of the Mongol Invasion), which depicts the valor of the Japanese side during the Genkō Invasions, is a recorded pictorial created by a single samurai, Takesaki Suenaga, to receive a reward. This scroll contains detailed depictions of samurai in tachi form, serving as a precious visual record of the sword equipment (wearing and装具 fittings) of the period.

Long-Term Effects of the Genkō Invasions on Samurai Society

Historical records directly proving that the Genkō Invasions shaped sword form are sparse. However, the following indirect effects can be identified.

Promotion of the Shift Toward Group Combat The recognition that organized collective combat was more important than individual prowess spread through samurai society, leading to the development of "infantry-focused group tactics" during the Nanbokuchō and Muromachi periods. This change provided one of the foundations for the "larger" and "practical" orientation of swords.

Strengthening of the Consciousness That "Japanese Swords Are Superior to Western and Asian Swords" The recognition spread that Japanese swords demonstrated high practical effectiveness in combat with the Mongol army, fostering a sense of "Japanese swords are supreme" in samurai society. This consciousness became one of the origins of the "Japanese sword superiority thesis" that continued into the Edo period and beyond.

Conclusion — How Foreign Impact Changed the Sword

The Genkō Invasions were a historical experience in which Japanese samurai confronted "unknown warfare." The Mongol army's group tactics, gunpowder weapons, and different combat ethics shook samurai assumptions and prompted a reassessment of sword form and use.

The trend of "enlargement and practicalization" in swords from the period immediately after the Genkō Invasions through the Nanbokuchō period cannot be understood apart from this foreign impact. To properly understand the history of Japanese swords, it is necessary to justly evaluate the importance of the Genkō Invasions as an external stimulus.