The Tsurugi Lineage — Double-Edged Swords From Bronze Age to Heian

What is the "Ken"? — Fundamental Differences from the Tachi and Katana

In modern Japanese, "ken" (剣) and "katana" (刀) are often conflated, but in sword history these two terms are strictly distinguished. "Ken" refers to a double-edged straight blade, while "katana" is single-edged with a curve. This difference in form reflects manufacturing techniques, purpose, and historical context.

The history of the "ken" in Japan begins with continental influence that brought bronze culture. During the Yayoi period (3rd century BCE to 3rd century CE), bronze ken brought from China and the Korean Peninsula were used for ritual purposes, after which iron straight blades became widespread as practical weapons.

Ken of the Yayoi and Kofun Periods — From Bronze to Iron

The bronze ken transmitted to the Japanese archipelago during the Yayoi period were used primarily in funerary and ritual contexts. From burial mounds in northern Kyushu (such as the Yoshinogari site), bronze ken have been excavated as grave goods, suggesting they functioned primarily as "symbols of power and sanctity" rather than as practical weapons.

With the Kofun period (3rd–7th centuries), the spread of iron-working technology made iron straight blades (sokantoōtachi, kondo-sōtachi, etc.) the mainstream of grave goods. The "sokantoōtachi" (素環頭大刀) was a straight blade with ring-shaped ornament at the tsuka-gashira (hilt pommel), inheriting continental forms while incorporating Japanese decoration. The Tokyo National Museum and Nara National Museum house numerous elaborate decorated straight blades from the Kofun period, conveying the political messages the rulers of that era invested in their swords.

The Nara and Heian Periods — From Tang-Style Straight Blades to Warabite-tō

During the Nara period (8th century), accompanying military system reforms under the ritsuryō state, double-edged straight blades modeled on Tang (Chinese) style ("tōyō-taichi") were adopted as principal weapons of the imperial military. Multiple straight blades from the Nara period are housed in the Shōsōin, serving as valuable materials attesting to cultural exchange with the continent.

In the early Heian period (around 9th century), through military campaigns against the Emishi (蝦夷) living in the northeast and Hokkaido, the distinctive "warabite-tō" (蕨手刀)—a blade with a pronounced curve—gained prominence. The warabite-tō featured a hilt pommel curved like fern fronds (warabite), and its curve is thought to have developed for ease of use in mounted combat. Many researchers view the warabite-tō as representing a transitional stage toward the later "tachi"—a single-edged, curved blade.

The "Kusanagi Ken" — The "Ken" of the Imperial Regalia

Discussing the "ken" in Japan inevitably involves the "Kusanagi-no-Tsurugi" (草薙剣), one of the Three Imperial Regalia of Japan (also known as Amanotsumurakumo-no-Tsurugi, 天叢雲剣).

According to the Kojiki and Nihon Shoki, the Kusanagi ken emerged from the body of Yamata no Orochi after Susanoo slew the serpent. It was later presented to Amaterasu Ōmikami and, through Jinmu Tennō's eastern conquest, entrusted to Yamato Takeru. Today, the Kusanagi ken is enshrined as the sacred object of Atsuta Shrine in Aichi Prefecture, and in principle, the general public is not permitted to view the actual blade.

Scholarly consensus holds that the Kusanagi ken was originally an iron straight blade, though its significance as a "sacred sword" and its religious and political implications have long been valued above the physical artifact itself. The Three Imperial Regalia, including the Kusanagi ken, serve as symbols of imperial legitimacy and continue to play a vital role in ceremonies attendant upon imperial enthronement.

Medieval Ceremonial Swords — "Kenji" and Samurai Protocol

In medieval samurai society, the "ken" held an important role not as a practical weapon but as a symbol of ritual and authority. The term "kenji" (剣璽) refers to the sword and seal (inkan) combined as symbols of imperial succession; among the shōgun and daimyō families, the ceremonial exchange of swords also took place.

By the Muromachi and Sengoku periods, a two-tiered system of "ceremonial tachi" and "practical uchigatana" became established. The "ken" (double-edged straight blade) survived chiefly as an enshrine blade in shrines and ritual implement for Shinto priests. Most "donated swords" (hōnōken) enshrined in shrines continue to follow the double-edged straight blade form, preserving the ancient ken's shape in the realm of faith.

The Modern "Ken" — Bamboo Swords and Wooden Swords in Kendo

The "shinai" (竹刀, bamboo sword) and "bokken" (木刀, wooden sword) used in modern kendo maintain etymological ties to the ken lineage. The shinai used in kendo competition adopts the form of a long straight blade without curve, spiritually inheriting the shape of the ancient "straight-bladed ken" prior to the tachi and uchigatana.

Furthermore, "ken" as Shinto implements continue to be crafted by metalworkers and sword smiths in the modern day. The production of donated swords demands high technical skill from sword makers due to the difficulty of forging double-edged blades, commanding prices ranging from hundreds of thousands to millions of yen.

Conclusion — The World Before the Japanese Katana, Revealed Through "Ken"

The history of "ken" (つるぎ) continues unbroken from the Yayoi period, when metal culture reached the Japanese archipelago, to the present day. Serving as a practical weapon, a symbol of authority, and an offering to the divine, it has persisted in Japanese culture, transforming with each era. Understanding the "age of straight blades" that precedes the curved world of the tachi and uchigatana is an indispensable perspective for comprehending Japanese sword culture from its continental and ancient origins onward.