Heian Period Japanese Swords — The Evolution from Straight Swords to Curved Swords

Chokutō (Straight Swords): Definition and Extant Masterpieces

A chokutō refers to a linear ancient sword with little to no curve in the blade. Japanese swords made from the Kofun period through the Nara period and early Heian period were generally of this type, and in sword classification they are distinguished from the "curved Japanese swords (wan-swords) with curvature from the mid-Heian period onward" and are called jokotō (ancient swords). It is common to distinguish those with a single edge as tachi (long sword), and those with double edges as ken (sword).

Representative extant chokutō include the following.

• Kingin denshō kara-tachi (Tang-style Straight Sword Decorated with Gold, Silver, and Mother-of-Pearl) — Shōsōin (Nara). A Tang-style straight sword decorated with gold, silver, and mother-of-pearl, transmitted as a relic associated with Emperor Shōmu.
• Shichiseiken (Seven Stars Sword) and Heishi Shōrinken (Heishi Pepper Forest Sword) — Shitennōji (Osaka). Straight swords from the Asuka period transmitted as being associated with Prince Shōtoku, both are National Treasures. The Shichiseiken bears a design of the Big Dipper.
• Suiryūken (Water Dragon Sword) — Tokyo National Museum. A Nara-period straight sword from the Shōsōin, known for having its mounting newly made as Emperor Meiji's worn sword during the Meiji period.

The differences between chokutō and Japanese swords (wan-swords) can be summarized as follows.

The Age of Continental Straight Swords — Sword Culture of the Nara Period

During the Nara period (710–794 CE) in Japan, sword culture was heavily influenced by continental China and the Korean peninsula. The swords in use at that time were called "tachi (long sword)" or "chokutō" — linear swords with single or double edges and little to no curve in the blade. These were largely imitative of Tang dynasty (618–907) methods, and many featured elaborate decorative mountings (koshirae), with their role as ceremonial and hierarchical symbols being more significant than their function as weapons.

The Shōsōin, an annex of Tōdaiji Temple in Nara, still preserves swords from the Nara period. The Shōsōin houses more than 50 old swords and ancient swords, bearing witness to the level of continental cultural adoption at that time and how swords functioned as symbols of authority in aristocratic society.

Why Did Curvature Emerge in Swords — Innovation in Metallurgy and Sword-Forging Techniques

The transition from straight swords to curved swords occurred gradually from the late Nara period through the early Heian period. At the core of this change was the development of Japan's unique ironworking and sword-forging techniques.

A transitional stage deserving attention is the "warabitetō (fern-handle sword)." Approximately 250 examples have been unearthed nationwide, with their concentration in Hokkaido and the Tōhoku region supporting the theory that they originated in the Kamitsuke region. The blades were relatively short, around 40 cm, and were made using "tomogane-zukuri (same-iron construction)," in which both edge and spine were carved from a single piece of iron. This technique was inherited by the subsequent "kenuki-gata tachi (tweezers-form long sword)," serving as an intermediate point in the morphological transition from continental-style straight swords to tamahagane composite-structure long swords. However, the theories that warabitetō were influenced by continental swords (Persian-style curved swords via China and the Korean peninsula) and that they developed indigenously within the Japanese archipelago remain in conflict, with no consensus yet established.

In the Japanese archipelago, a unique ironworking method called "tatara smelting" developed, enabling the production of "tamahagane (ball steel)" from iron sand. Tamahagane, created by combining multiple steels with different carbon contents, made it possible to achieve blades that were both hard and tough. The structure of placing hard edge-steel (hagane) on the outside and resilient core-iron (shinagane) on the inside achieved both sharp cutting ability and resistance to breakage.

An equally important technical innovation was the establishment of the tempering method called "tsuchi-oki (clay placement)." The swordsmith applied refractory clay thinly to the blade edge and thickly to the spine side, heated the entire piece to high temperature, then plunged it into water for rapid cooling. During this process, the blade edge contracts rapidly, while the clay-covered spine side cools gradually, creating a natural curve across the entire blade — the "sori (curvature)." Curvature was not merely an aesthetic choice but also a result of technical necessity in pursuit of superior blades. Simultaneously, this process produced the distinctive pattern along the edge called "hamon (hardening line)." This pattern would later become central to the aesthetic appreciation of Japanese swords.

Mounted Warfare and the Birth of Tachi — Combat Shaped the Sword

By the mid-Heian period (9th–10th centuries), through conflicts with the Emishi in the Tōhoku region and local strife, mounted mobile warfare became Japan's primary combat style. This development fundamentally changed the functional requirements for swords.

Straight swords had a physical disadvantage when attacking from horseback. Striking with a linear blade tends to result in a pushing action rather than efficient cutting, diminishing cutting force. Conversely, curved swords trace an arc in the downstrike, achieving substantial cutting force through "hikigiri (draw-cutting)" — slashing while pulling the blade. This was an ideal characteristic for mounted swordplay.

The curved sword born from this need is the "tachi (long sword)." The tachi was worn as a "hakeru" sword, suspended edge-down from the left side of the waist by a leather cord (kawaō). This carrying method, differing from the later "sasu" style where swords were worn edge-up on the waist belt, was a practical approach that allowed easy drawing even from horseback with longer blades.

The "Kogarasumaru (Small Crow)" is known as one of the earliest extant curved swords, displaying a distinctive form with curvature from the mid-blade to the tip. Currently held by the Imperial Household Agency, this sword is noted by sword scholars as a valuable material artifact symbolizing the transition from straight swords to tachi.

During the transitional period from the late Heian to early Kamakura period, the tachi form itself underwent significant changes. The characteristic "fukura-gare (tapered swell)" of Heian-period tachi — a slightly narrow and elegant kissaki (point) — gave way to the "inokubi-kissaki (boar-neck point)" of the early Kamakura period, which was shorter and more robust. This change was linked to the practical demand for precisely piercing gaps in armor, demonstrating how shifts in combat tactics were reflected even in the fine details of blade form.

The Rise of the Samurai Class and the Deepening of Sword Culture

In the late Heian period (11th–12th centuries), regional armed groups — the samurai (bushi) — began to rise. While the Fujiwara clan controlled court politics, samurai groups maintaining security in remote regions and protecting estates rapidly gained power. The rivalry between the two great samurai clans, the Minamoto (Genji) and the Taira (Heike), culminated in the Genpei War (Genpei no Ran) of 1180–1185, and through major land and naval battles at Ichinotani, Yashima, and Dannoura, tachi emerged as the primary weapon in actual combat on the historical stage.

In this era, the sword transcended mere weaponry for the samurai. Fine swords were inherited as family treasures across generations, and accomplished swordsmiths enjoyed special status and renown. The "Mikazuki Munechika (Crescent Moon Munechika)," attributed to the swordsmith Sanjō Munechika who was active in Kyoto in the late Heian period, is an elegant tachi with crescent-shaped nie floating on the blade surface, later counted among the "Tenka Goken (Five Swords Under Heaven)." Currently housed in the Tokyo National Museum, this renowned blade transmits the aesthetic and technical pinnacle of Heian sword-forging to the present day.

Frequently Asked Questions (FAQ)

Are Chokutō Included in Japanese Swords?

While "Japanese sword" is sometimes used broadly to refer to all swords made in Japan, in formal sword classification, "Japanese sword" specifically denotes wan-swords from the mid-Heian period onward that are made of tamahagane and feature curvature and shinogi-zukuri (ridge construction), while earlier straight swords are distinguished as "jokotō (ancient swords)."

Were Swords the Only Weapons of the Heian Period?

The primary weapon was actually the bow and arrow. From the mid-Heian period onward, samurai combat centered on "kishaw (mounted archery)," with tachi serving as a weapon for close combat and grappling. Additionally, naginata (halberd) developed as an infantry weapon.

Where Can I See Chokutō Today?

The "Shōsōin Exhibition," held annually each autumn at the Nara National Museum, features swords from the Shōsōin in certain years. The Shichiseiken and Heishi Shōrinken of Shitennōji (Osaka) are occasionally displayed at the temple's treasure hall, and the Tokyo National Museum also houses and displays ancient swords such as the Suiryūken.

Conclusion — The Era When the Prototype of Japanese Swords Was Formed

The centuries spanning the Nara through Heian periods were decisive in the establishment of the prototype for Japanese swords. Straight swords transmitted from the continent were transformed into curved tachi through innovation in Japan's unique metallurgy and sword-forging techniques and adaptation to mounted warfare tactics. This evolution was not a matter of chance, but a historical inevitability resulting from the complex interplay of three forces: practical demands of combat, technical innovation, and the rise of a new social class — the samurai.

The ornate straight swords resting in the Shōsōin and the tachi gleaming upon the waves of Dannoura — separated by mere centuries, these embody Japan's great historical and cultural transformation. As of 2026, the renowned swords of this era can be viewed in person at the Tokyo National Museum and sword museums throughout the country, allowing visitors to experientially understand the profound reasons Japanese swords have been transmitted as artworks and spiritual symbols transcending mere weapons.