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

What Was the Mongol Invasion?—Two Foreign Military Invasions

In 1274 (Bunei 11) and 1281 (Kōan 4), coalition forces 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 threat in Japanese history and had a profound impact on the Kamakura shogunate and the samurai. Detailed historical background is also explained in Mongol Invasion and the Sword Revolution.

While the Mongol Invasions are known militarily for the invading forces' retreat due to typhoons (kamikaze), the experience of close combat and archery battles over several days brought definite changes to the samurai society's view of warfare and weapons.

Mongol Military Tactics—The "Foreign War" Japanese Samurai Faced

The combat of samurai in the Kamakura period was based on mounted archery with the bow as the primary weapon and one-on-one sword duels with formal declarations. In contrast, Mongol military tactics were fundamentally different.

• Group Tactics (Dense Formations): Mongol forces had infantry move in tightly packed formations, acting in unison at signals from drums and gongs. Their tactics, which prioritized group coordination over individual prowess, brought confusion to Japanese samurai who expected one-on-one combat.
• Use of Gunpowder Weapons (tetsuhau): There are records of explosive projectiles called "tetsuhau" being used. The blast and flash frightened horses and negated samurai cavalry charges. This weapon was the first gunpowder weapon Japanese samurai had encountered, and its psychological impact was immeasurable.
• Poisoned Arrows and Volley Fire: Mongol bows were shorter than Japanese bows with shorter range, but excelled at massed area suppression fire. Records also document the use of poisoned arrows (Mongol arrows), and some wounded samurai were unable to recover from their injuries.

Direct Impact of the Mongol Invasions on Japanese Swords—From Historical Records and Archaeology

The Problem of Sharpness—The Relationship Between Mongol Armor and Japanese Swords

During the Bunei Invasion, there are multiple records of Japanese samurai saying "we cut the Mongol soldiers with the tachi, but it did not cut" (such as in the 'Hachiman's Mongol Records'). This can be attributed to the following factors.

• Heavily Armored Mongol Soldiers: The infantry of the Yuan forces wore armor similar to "belly plates" and chain mail. Though smaller than the armor Japanese samurai expected, it was designed to resist thrusting more than cutting. The requirement for the tachi to prioritize thrusting over cutting may have influenced later sword shape changes.
• Blade Damage: After fierce battles with the Mongol forces, there are also records of "swords breaking" and "blades chipping." Some theorize that this influenced later blade strengthening (increased kasane and weight).

Post-Mongol Invasion Sword Shape Changes—From Archaeological and Rubbing Records

After the Mongol Invasions (Bunei and Kōan Invasions: 1274–1281), the following changes are observed in swords from the late Kamakura period (late 13th to early 14th centuries).

• Trend Toward Larger kissaki: A shift from the typical pre-Mongol "inokubi kissaki" to larger kissaki is observed. As the kissaki becomes larger, thrusting ability improves—some researchers interpret this as a change to counter Mongol group close-combat tactics.
• Increase in kasane: A trend of increasing blade thickness (kasane) is observed. In Mongol group close-combat, swords repeatedly contacting shields and armor would easily chip or break. This experience may have raised demands for durability and influenced the trend toward thicker and heavier blades.
• Acceleration of Bizen and Sōshū Tradition Fusion: From the late Kamakura period through the Northern and Southern Courts period, the powerful boiling-effect hamon of the Sōshū tradition, represented by Masamune, became popular. This trend coincides with the historical context where the impact of the Mongol Invasions heightened interest in "practical strength."

The "Mongol Invasion Sword" Legend—Reality and Mythologization

Many swords and anecdotes claimed to be related to the Mongol Invasions appeared in later times. However, most remain in the realm of legend.

• Collection of "Mongol Swords": Some weapons and armor left by the Mongol forces were brought back as spoils of war by samurai and temples. Records exist of Mongol-made swords (curved swords, saber-type blades) flowing into Japan and being treasured as "imported swords." Some of these are said to be housed in museums and temples today, but few swords can be definitively identified as Mongol Invasion-related.
• Takezaki Suenaga's Valor and the Sword: The scroll painting "Mongol Invasion Picture Scroll (Mōko Shūrai Ekotoba)," which depicts the Japanese side's brave efforts during the Mongol Invasions, is a pictorial record commissioned by a single samurai named Takezaki Suenaga to gain a reward. The scroll contains detailed depictions of samurai wielding the tachi, making it a precious visual record of the sword mounting style (wearing method and construction) of the period.

Long-Term Impact of the Mongol Invasions on Japanese Samurai Society

There are few historical records proving that the experience of the Mongol Invasions directly changed sword shapes. However, the following can be pointed out as indirect influences.

• Promotion of a Shift Toward Group Warfare: The understanding that organized group combat was more important than individual valor spread through samurai society, leading to the development of "infantry-centered group tactics" during the Northern and Southern Courts to Muromachi period. This change is one of the underlying factors behind the tachi's "increase in size" and "emphasis on practicality."
• Strengthening of the Belief that "Japanese Swords Are Superior to Western and Asian Swords": The understanding spread that Japanese swords demonstrated high practicality in combat with the Mongol forces, fostering a self-awareness among samurai society that "Japanese swords are supreme." This consciousness became one of the origins of the "Japanese sword superiority theory" that continued into the Edo period and beyond.

Conclusion—Foreign Impact Changed the Sword

The Mongol Invasions were a historical experience where Japanese samurai faced "unknown warfare." The Mongol forces' group tactics, gunpowder weapons, and different combat ethics shook samurai views of warfare and prompted a reconsideration of sword shapes and usage.

The trend of swords becoming "larger and more practical" from immediately after the Mongol Invasions through the Northern and Southern Courts period cannot be discussed without this foreign impact. To understand the history of Japanese swords, it is necessary to properly evaluate the importance of the Mongol Invasions as an external stimulus.

If you wish to see the actual swords of this era, you can also search for works from the late Kamakura period onward in the online catalog.