Bun'ei Campaign — The Mongol Invasion and the Swords of Kamakura Warriors

The Bun'ei Campaign was an incident in which, in the 10th month of Bun'ei 11 (1274), the Yuan–Goryeo allied army dispatched by Kublai Khan, Emperor of the Yuan (Mongol Empire), invaded northern Kyushu. In Japan it is known as the first invasion of the Genkō (Mongol Invasions), and it is often discussed together with the second invasion of Kōan 4 (1281), the Kōan Campaign. However, viewed from the perspective of the battle course of the Bun'ei Campaign alone and its impact on swords, it merits discussion as an independent, epoch-making event in Japanese history.

Kublai Khan's Plans for an Expedition to Japan and Background

In the late 13th century, the Yuan Empire under Kublai Khan controlled most of the Eurasian continent and sought to expand its hegemony over East Asia. From Bun'ei 5 (1268) onward, Kublai sent envoys to Japan several times demanding tribute and submission. Hōjō Tokimune, the eighth shikken (regent) of the Kamakura shogunate, firmly rejected these demands and took a hard line by refusing to send a reply. Tokimune became regent at only eighteen, and as a young politician he turned away Yuan pressure without any compromise.

In the 10th month of Bun'ei 11 (1274), the Yuan–Goryeo allied army set out on Kublai's orders. This great force, made up of Yuan troops (Mongol and Han Chinese) and Goryeo troops, including sailors, is estimated at roughly 27,000 to 40,000 men. Boarding 726 to 900 warships, they passed through Tsushima and Iki and landed in Hakata Bay on the 20th day of the 10th month of Bun'ei 11 (1274).

Course of Battle — Tragedy at Tsushima and Iki and the Decisive Fight at Hakata Bay

Early in the 10th month of Bun'ei 11 (1274), the Yuan–Goryeo allied army first landed on Tsushima. The deputy constable Sō Sukekuni fought with some eighty mounted warriors against the roughly 1,000 Yuan troops who had landed, and after a valiant fight he fell in battle. The deputy constable of Iki, Taira no Kagetaka, also fought bravely with a small force, but the island of Iki was subdued. The island's inhabitants were ruthlessly killed or taken away, and the devastation was passed down to later generations.

On the 20th day of the 10th month of Bun'ei 11 (1274), the Yuan–Goryeo allied army landed in Sawara District on the western side of Hakata Bay (including Momochibara), although there are various theories about the exact landing site. The commander-in-chief Shōni Kagesuke and the Constable of Bungo, Ōtomo Yoriyasu, together with the forces of Kyushu gokenin (vassal housemen), resisted, but they struggled against the Yuan group tactics, short bows, poisoned arrows, and gunpowder weapons (tetsuhau). The Yuan army used drum signals to advance, retreat, and shoot en masse in tight formations, overwhelming Japanese forces who valued individual martial skill.

The tetsuhau (a mixed projectile of explosive gunpowder, stone shot, and incendiary materials) was the first gunpowder weapon the Japanese warriors encountered. Records describe horses startled by the explosions, flashes, and poisonous smoke, and warriors thrown into confusion. The Yuan forces occupied and set fire to the town of Hakata, and the Japanese troops retreated to the area near Mizuki in Dazaifu.

However, after the difficulties of the fighting and the wounding of deputy commander Liu Fuheng, the Yuan army decided in a war council to withdraw, and by the morning of the 21st day of the 10th month of Bun'ei 11 (1274) it had vanished from Hakata Bay. On the return voyage to Goryeo it met a storm, and many of its ships sank or were damaged. Japanese deaths and captives were numerous, but the Yuan also lost many troops and ships, and the first invasion ended in failure.

Practical Superiority and Limits of Swords — From Single Combat to Massed Battle

The combat style and swords of the Japanese warriors in the Bun'ei Campaign stood in sharp contrast to the Yuan group tactics. The principal weapons of Kamakura warriors were bows and arrows and the sword (tachi), and in close combat they used the tachi. Kamakura-period tachi had shinogi-zukuri construction and shifted from the early, elegant form with deep koshizori to the broad-bodied, imposing form of the middle period onward. The 'Kamakura blades' made by smiths of Bizen, Yamashiro, and Yamato embodied the highest cutting technology of their era.

In one-on-one close combat with the Yuan, the Japanese tachi displayed overwhelming cutting power. However, against the Yuan's group tactics of dense infantry with shields pushed to the front, the Japanese tachi, the essence of individual martial skill, also had certain limits. To achieve the refined qualities of 'not breaking, not bending, and cutting well,' Japanese tachi were differentially hardened so that the edge (hamon) and the back (jigane) had different hardness.

There is a view that the experience of the Mongol Invasions spurred later changes in swords. From the late Kamakura to the Nanboku-chō period, broad-bodied tachi with little difference between the width at the base and at the tip, and with large kissaki (points), became popular. Smiths such as Mitsutada, Nagamitsu, and Sanenaga of Osafune, the Rai school of Yamashiro, and Tegai Kanenaga of Yamato were active in this period.

Takezaki Suenaga and the Mōko Shūrai Ekotoba — A Living Record of Warriors Bearing Swords

An indispensable primary source for the Bun'ei Campaign is the Mōko Shūrai Ekotoba (Illustrated Account of the Mongol Invasions), commissioned by Takezaki Suenaga, a gokenin of Higo Province (present-day Kumamoto Prefecture). This emaki is a contemporary record depicting Suenaga's own valiant fighting in the two campaigns of Bun'ei and Kōan, and it is the most important source for understanding the attire, arms, and fighting styles of Kamakura warriors. It is a National Treasure held by the Museum of the Imperial Collections, Sannomaru Shozokan. The ekotoba depicts in detail warriors holding tachi, the explosion of the Yuan's tetsuhau, mounted charges, and the chaos of group battle, visually conveying the actual use of swords in the Bun'ei Campaign. The scene in which Suenaga charges into the Yuan forces on horseback is especially well known as a celebrated image of the personal bravery of Kamakura warriors.

The Bun'ei Campaign is an event that demonstrated the important function of 'self-renewal through actual combat' in the history of Japanese swords. Facing unknown enemies and tactics, Kamakura smiths deepened their techniques and further raised the completeness of later Japanese swords. In this sense, the Bun'ei Campaign is positioned not merely as an event of military history but as a critical trial and an opportunity for innovation in the technical history of Japanese swords. The stimulus this battle gave, together with the experience of the Kōan Campaign (1281), laid the foundation for the golden age of sword art from the late Kamakura to the Nanboku-chō period.

Stone Walls Built after the Mongol Invasions and the Preparedness of Kamakura Warriors

Drawing on the experience of the Bun'ei Campaign, the Kamakura shogunate mobilized all its strength to strengthen the defense of Kyushu. In preparation for the second invasion, the Kōan Campaign of Kōan 4 (1281), stone walls (Genkō Bōrui) extending about 20 km were built along the shores of Hakata Bay. This construction was a forced corvée assigned to the gokenin of the Kyushu provinces, and its cost and labor were enormous. The walls actually had a certain effect in preventing Yuan landings during the Kōan Campaign, and together with a storm (kamikaze, the divine wind) they contributed to repelling the second invasion.

In Osafune in Bizen Province (present-day Setouchi City, Okayama Prefecture), the outstanding smiths Mitsutada, Nagamitsu, Sanenaga, and Kanemitsu succeeded one another in their work, establishing the fame of 'Bizen Osafune' throughout the country. Many masterpieces of tachi made in this period survive today, and many are designated Important Cultural Properties or Important Art Objects.