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

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

In modern Japanese, it is not uncommon to confuse "ken" (ken) and "katana" (katana), but in sword history, these two terms are strictly distinguished. "Ken" refers to double-edged straight swords, while "katana" has a single edge and a curve. This difference in form reflects manufacturing techniques, use, and historical context.

The history of "ken" in Japan begins with the influence of continental culture that brought bronze crafting. 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, and subsequently iron straight swords 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 burial and ritual contexts. Bronze ken have been excavated as grave goods from Yayoi burial mounds in northern Kyushu (such as the Yoshinogari site), and it is believed that their primary role was as a "symbol of power and sacredness" rather than as a functional weapon.

With the entry into the Kofun period (3rd–7th century), iron straight swords (such as sokantō-tachi and kintō-sōtachi) became the mainstream grave goods as ironworking technology spread. The "sokantō-tachi" (straight sword with ring-shaped pommel decoration) was a straight sword with ring-shaped decoration on the pommel, inheriting its form from the continent while being enhanced with Japanese aesthetic elements. The Tokyo National Museum and the Nara National Museum house numerous luxurious kintō-sōtachi from the Kofun period, conveying the political messages that the royal power of that era embedded in swords.

Nara and Heian Periods—From Tang-Style Straight Swords to Warabitetō

During the Nara period (8th century), alongside the reorganization of the military system of the ritsuryō state, double-edged straight swords modeled on Tang (Chinese) style ("Tōyō-tachi") were adopted as the primary weapons of the imperial army. The Shōsōin houses multiple straight swords from the Nara period, serving as valuable materials demonstrating cultural exchange with the continent.

In the early Heian period (around the 9th century), the distinctive curved warabitetō gained prominence through combat with the Emishi (indigenous people) living in the northeast and Hokkaido. The warabitetō had a pommel shaped like the young fronds of a bracken fern, and its curve is thought to have developed for ease of use in mounted combat. Many researchers view this warabitetō as representing one stage in the transition to the later "tachi"—single-edged curved swords.

"Kusanagi Sword"—The "Ken" Among the Three Imperial Regalia

Unavoidable in any discussion of the Japanese "ken" is the "Kusanagi Sword" (Kusanagi no Tsurugi, or Amanomurakunotetsugi), one of the Three Imperial Regalia of the imperial family.

According to myths in the Kojiki and Nihonshoki, the Kusanagi Sword is said to have been transmitted as follows:

1. When Susanoo defeated Yamata no Orochi, the Kusanagi Sword emerged from within its body
2. It was offered to Amaterasu Ōmikami
3. It was transmitted to Ninigi as one of the Three Imperial Regalia
4. It was moved to Ise Grand Shrine during the reign of Emperor Sujin
5. It was bestowed upon Yamato Takeru through Yamato Hime

Currently, the Kusanagi Sword is enshrined as the sacred object of Atsuta Jingu in Aichi Prefecture, and the general public is in principle not permitted to view the actual object.

There are various theories about the true nature of the Kusanagi Sword, with the view that it is an iron straight sword being most prominent, but its significance as a "divine sword" in terms of faith and politics has long been valued over the physical object itself. The Three Imperial Regalia, including the Kusanagi Sword, serve as symbols of imperial legitimacy and continue to play an important role in imperial enthronement ceremonies to this day.

Medieval Ritual Swords—"Kenji" and Samurai Etiquette

In medieval samurai society, "ken" played an important role primarily as a symbol of ritual and authority rather than as a practical weapon. The term "kenji" refers to symbolic objects of imperial succession combining a sword and seal (stamp), but ritual transfer of swords was also practiced among shogunal and daimyo families.

During the Muromachi and Sengoku periods, a two-tier structure of "ritual tachi" and "practical uchigata" became established, and "ken" (double-edged straight swords) survived primarily as votive swords dedicated to shrines and ritual implements for shrine priests. Most "hōnōken" (votive swords) dedicated to shrines follow the form of double-edged straight swords, preserving the ancient form of "ken" in the realm of faith.

The Modern "Ken"—Wooden Swords in Kendo

The "bamboo sword" (shinai) and "wooden sword" (bokken) used in modern kendo are etymologically descended from "ken". The "bamboo sword" used in kendo competitions is fundamentally shaped like a long, straight sword (without curve), spiritually inheriting the form of the ancient "straight-sword ken" from the earlier tachi and uchigata.

Moreover, "ken" as shrine implements continue to be crafted by metalworkers and swordsmiths in the present day. The manufacture of votive swords requires the high skill of swordsmiths due to the difficulty of creating double-edged blades, and they are traded at prices ranging from several hundred thousand to several million yen.

Conclusion—The World Before the Japanese Sword, as Told by "Ken"

The history of "ken" (straight sword) continues unbroken from the Yayoi period, when metalworking culture was transmitted to the Japanese archipelago, to the present day. It has persisted in Japanese culture through the ages as a practical weapon, a symbol of authority, and an offering to the gods, taking on different forms in each era. Understanding the "era of straight swords" that preceded the world of the curved "tachi" and "uchigata" is an essential perspective for comprehending Japanese sword culture from the continent and ancient times.