The Sword Revolution of the Nanbokucho Period: Why the Great Tachi and Field Swords Emerged

The Upheaval of the Nanbokucho Era and the Sudden Transformation of Swords

In 1336, Ashikaga Takauji established the Muromachi shogunate in Kyoto by enthronement of Emperor Komyo, while the deposed Emperor Go-Daigo fled to Yoshino to found the "Southern Court." The resulting sixty-year standoff between Southern and Northern courts was one of the most intense civil wars in Japanese history, involving sustained large-scale combat across the entire country.

This upheaval had a dramatic effect on sword form. From the end of the Kamakura period through the Nanbokucho era, Japanese swords underwent the most extensive enlargement in their history. The tachi, whose standard blade length was around two shaku (approximately 60 cm), evolved into the o-tachi (great tachi) with blades exceeding three shaku (approximately 90 cm), and further into the nodachi (field sword) and the "carrying tachi" large enough to be slung on the back.

Why Swords Grew Larger: The Tactical Background

The enlargement of swords during the Nanbokucho period had multiple tactical and social causes.

The shift to mass infantry combat: The earlier model of individual mounted-warrior duels gave way to large-scale battles fought by dense groups of foot soldiers (kachi-shu). When foot soldiers needed to deliver powerful downward strokes against packed enemy formations, longer-reach swords were advantageous.

Naginata-like use: The o-tachi was sometimes wielded in a manner similar to the naginata (curved polearm)—sweeping low to slash horses' legs or cutting across wide swaths of densely grouped enemies.

The prolonged and large-scale nature of the fighting: Over sixty years of continuous warfare, armor improved steadily, and more powerful slashing strikes were demanded. A longer blade generates greater centripetal force, enhancing the impact against heavy armor.

Master Smiths and Famous Swords of the Nanbokucho Period

This era also produced some of the greatest masterpieces in all of Japanese sword history.

Osafune Kanemitsu is the defining master of the Bizen Osafune school in the Nanbokucho period. Many of his o-tachi survive as National Treasures and Important Cultural Properties; their overwhelming presence and consummate beauty continue to captivate collectors and historians to this day.

The lineage of Soshu Masamune: Masamune himself worked in the late Kamakura period, but his students flourished in the Nanbokucho era. Sadamune and Go no Yoshihiro stand at the summit of the Soshu tradition and are still considered the highest achievements of the school, prized for the beauty of their nie (large crystalline martensite particles) and the depth of their jigane.

The Rai school (Yamashiro) and the Aoe school (Bitchu) also produced many important swords during the Nanbokucho period.

The Practice of Suriage: Bridging the Edo Period

Many of the great tachi produced in the Nanbokucho era were later subjected to suriage (shortening)—a process of reducing blade length to make them more practical for later standards. This was typically carried out in the Edo period.

As a result of suriage, part or all of the original nakago (tang) was removed, and the maker's signature was frequently lost. Consequently, many surviving Nanbokucho-period great swords are classified as "suriage mumei" (shortened and unsigned), and determining the true maker is a major challenge in connoisseurship.

The Bridge to the Sengoku Period

When the Nanbokucho conflict came to a nominal end in 1392, Japan entered the relatively stable middle Muromachi period. However, with the Onin War of 1467, more than a century of Sengoku (Warring States) warfare began again, and the Japanese sword evolved along yet another path.

The o-tachi and nodachi of the Nanbokucho period are more than merely "large swords." They are witnesses to history—embodying the spirit of warriors in a fractured age and the memory of battles fought at the cost of life itself. The overwhelming presence of these great swords displayed in museums speaks powerfully across seven hundred years, summoning the intensity of that violent era into the present.