Before the Tachi: Swords of Japan's Kofun, Asuka, and Nara Periods and the Origins of the Japanese Sword

The Era of Straight Swords—From the Kofun to Nara Period

Before the modern concept of "Japanese sword" was established, swords that existed in the Japanese archipelago can be broadly divided into two traditions. One is the technology of straight swords (chokutou) transmitted from the Korean Peninsula and China, and the other is the tradition of curved swords (wantou) that developed uniquely in the Japanese archipelago.

From the Kofun period through the Asuka period (3rd–7th centuries), straight swords were the mainstream type of sword used by Japan's ruling class. These swords, with straight blades and single-edge or double-edge construction, originated from Chinese sword-making techniques of the Han and Three Kingdoms periods and were transmitted to Japan via the Korean Peninsula. Most iron swords excavated from burial mounds are straight swords, and for the ruling class of the time, they served as both symbols of power and practical weapons in combat.

Manufacturing techniques for straight swords were strongly influenced by China, but they gradually changed through use in the Japanese archipelago. Many elements were "Japanized," including the proportioning of thickness between the edge and spine, the proportions between the grip and blade, and methods for crafting fittings such as handles and scabbards. However, the straight swords of this period still bore the strong character of "imitation of foreign technology."

The Emergence of Curved Swords—From the Nara Period to the Early Heian Period

From the 8th to the 9th century, dramatic changes came to sword-making in the Japanese archipelago—the transition from straight to curved swords.

Behind this change lies the development of a uniquely Japanese combat style. As mounted combat became the main mode of warfare, demand increased for swords that possessed "greater cutting power and were easier to draw." Curved swords (particularly those with curvature) were the optimal form for striking enemies in mounted combat, and this military necessity drove the change in form.

At the same time, manufacturing techniques were evolving. Techniques such as "repeated forging" and "differential hardening" for controlling the hardness and flexibility of iron were refined, enabling the creation of stronger and more durable swords. While these techniques were based on knowledge from China and Korea, they evolved in unique directions through trial and error within Japan.

Consolidation into the Tachi—From the Mid to Late Heian Period

From the 10th to 11th centuries, during the mid-Heian period, the Japanese sword reached a complete form as the "tachi."

The tachi typically refers to a sword with "a blade length of 70cm or more, deep curvature, maximum thickness at the center of the blade, and gradual tapering toward the point." The mounting method known as "suspended tachi," hung from the scabbard and suspended from the belt, became standard equipment for mounted warriors (samurai).

During this period, sword-making became systematically practiced by groups of specialists known as "toukou" (swordsmiths). Groups of sword forgers formed in regions blessed with iron resources and water, such as Yamashiro Province (present-day Kyoto Prefecture), Sagami Province (present-day Kanagawa Prefecture), and Bizen Province (present-day Okayama Prefecture), each developing their own unique techniques and styles. It is also significant that during this same period, signatures of swordsmiths, called "mei," began to be carved into the blade, making the individuality and skill of the smith clearly identifiable.

Functional Design of the Tachi—The Role of Curvature

The greatest characteristic of the tachi is the presence of "curvature (sori)." This curvature was not merely an aesthetic choice, but the result of highly refined functional design.

A curved blade maximizes cutting efficiency in mounted combat. When striking an enemy from horseback, the curvature of the blade naturally makes "the contact surface against the enemy's shoulder or arm nearly perpendicular, increasing the penetrating power of the cut." Furthermore, upward cuts from below become easier to execute, and attacks that avoid the opponent's armor and shields become more feasible.

Furthermore, curvature contributes to "operational efficiency during quick draws." The motion of drawing a curved blade from its scabbard is smoother than a straight blade, and by the moment the draw is complete, the cutting stance is already fully formed. This characteristic, which reduces time loss in combat, was extremely important in real combat situations where life and death hung in the balance.

Technical Perfection—Jihada, Hamon, and Forging

During the era of the tachi, many aesthetic and technical characteristics of the Japanese sword became established.

Jihada—the pattern visible across the entire blade—is created by repeatedly folding and forging. The varied patterns of jihada are the result of intentional forging by the craftsman, and identifying these patterns provides important information for determining the smith and period.

• mokume
• itame
• masame

Hamon—the wavy pattern visible on the cutting edge—is created by carbon concentration during quenching. The pattern of the hamon is the most important indicator of the smith's school and period.

• suguha
• choji hamon
• gunome hamon
• midare hamon

Many of these technical characteristics became perfected during the era of the tachi (10th–13th centuries) and formed the foundation for the subsequent development of the Japanese sword.

From Tachi to Uchigatana—The Reconfiguration of Combat Style

The era in which the tachi reigned as the perfected form eventually came to an end. With the arrival of the Sengoku period (15th–16th centuries), combat methods changed dramatically once again.

In the Sengoku period, when group combat became the main form of warfare, the importance of mounted combat declined, and tightly formed infantry formations and strikes over armor became predominant. In response to these changes, swords also evolved, with the "uchigatana"—worn in the "thrust-draw" style suspended from the belt—becoming the new standard. The transition from tachi to uchigatana was another major technological shift that reflected changes in combat environment into sword design.

From the straight swords of the Kofun period, to the tachi of the Heian period, to the uchigatana of the Sengoku period—the history of the Japanese sword is the story of a sword culture that continually evolved in form and function in response to the demands of the era while always remaining a practical weapon of war.