Continental Sword Imports in the Asuka Period: Tang and Baekje Blade Technology

Asuka Period and Continental Cultural Waves—the "Import Period" in Sword History

When discussing the history of the Japanese sword, it is often recounted from the curved blade (tachi with sori) that was born in the Heian Period. However, the history of swords and blades in Japan began in an era far earlier than that, and the Asuka Period (approximately 592–710) is positioned as a particularly noteworthy "period of active import of continental technology."

Centered on the era of Empress Suiko (r. 593–628) and Prince Shōtoku, Japan actively advanced diplomatic and cultural exchanges with China's Sui and the kingdoms of Baekje, Goguryeo, and Silla on the Korean Peninsula. Since the Tang was founded in 618, the Chinese dynasty with which the Suiko court directly exchanged was the Sui (until 618). Formal diplomatic relations and technological reception from the Tang began with the first official mission to Tang in 630 and unfolded from the Nara Period onward. The international relations of this era were not merely political contact, but also a massive project to transplant advanced civilizational elements—metallurgical technology, forging technology, Buddhist culture, and more—to the Japanese archipelago.

In this article, we will examine the sword and blade technology that flowed into Japan from the continent during the Asuka Period and the impact it had on the later development of the Japanese sword.

Before the Asuka Period—The Sword and Blade Situation of the Kofun Period

To understand the imports of the Asuka Period, we must first grasp the situation of the Kofun Period (late 3rd century to around the 7th century), which provides its foundation.

In the Kofun Period of Japan, numerous iron swords and iron blades were unearthed as grave goods. Notable examples include the gold-inlaid iron sword (National Treasure) discovered at the Inariryama Kofun in Saitama Prefecture and the iron blade from the Etafunayama Kofun in Kumamoto Prefecture. These are all straight blades (chokutō)—blades without curve, with straight edges—and show strong influence from the daoshi and kantoō tachi that were widely manufactured on the Chinese continent and Korean Peninsula.

Iron tool production in the Kofun Period was largely carried out by blacksmith craftsmen (kajishi) who came from the Korean Peninsula, and Japan's own blacksmithing techniques were still in their nascent stage. It is believed that technological transfer from the continent substantially supported Japan's iron tool industry during this era.

The Diplomatic Policy and Technological Transfer of the Suiko Court

Dispatching Missions to Sui and Tang

Under the leadership of Prince Shōtoku, the Suiko court dispatched the first mission to Sui (Ono no Imoko) in 607. After the collapse of Sui, it was succeeded by missions to Tang (first dispatched in 630) and implemented continuously throughout the Nara Period.

The purpose of the missions to Sui and Tang was not merely to obtain political recognition. The accompanying students and scholarly monks learned the following knowledge and techniques from China and returned home.

• Legal and administrative systems
• Buddhism
• Confucianism
• Medicine
• Astronomy
• Craft techniques and metalworking (including Tang-era sword and blade technology)

Particularly noteworthy is Tang-era sword and blade technology. Tang-era swords and blades were called karatachi and karayō daoshi, and they represented the world standard of the time in steel refining techniques and tempering technology.

Blacksmithing Technology Transfer from Baekje

Equally important alongside the routes of missions to Sui and Tang is direct technological transfer from Baekje (present-day western Korean Peninsula). From the late 6th century to the early 7th century, Baekje maintained close relations with Japan as a conduit for the spread of Buddhist culture. According to records, when Buddhism was officially transmitted in 552 (or 538), among the technicians who came from Baekje to Japan were blacksmiths (kajishi).

The Nihon Shoki contains multiple articles showing that "Buddhist texts" and "technicians" were sent from Baekje. These immigrant-descended blacksmiths were organized as "kajibe" (blacksmith groups) and undertook the production of weapons, agricultural tools, and implements under the Yamato regime.

Content of Sword and Blade Technology That Flowed Into the Asuka Period

Steel Refining Technique

Iron tool production in pre-Asuka Japan was centered on the method of forging sponge iron obtained by reducing sand iron at low temperatures. This resulted in unstable carbon content and made it difficult to produce uniform steel.

The techniques transmitted from the continent included early forms of blast furnace technology and methods of controlling carbon content to produce "steel." In Tang-era China, a refining method called "hundred-times-refined steel" had developed, and a technique had been established in which iron was repeatedly forged to remove impurities and obtain high-quality steel.

This technique became the prototype for iron production technology that would later develop into Japan's unique tatara smelting.

Early Form of Tempering Technology

One of the greatest characteristics of the Japanese sword is "tempering"—a technique of rapidly cooling only the blade edge to harden it. The original form of this tempering technique is believed to have been brought about through technological transfer from the continent.

In Tang-era China, a primitive form of "doki" was known—applying clay to the blade section and rapidly cooling it to harden only the edge without covering the entire blade. When this was transmitted to Japan and later underwent independent development, it became the predecessor of the hamon that master craftsmen of the Kamakura Period would perfect.

Development from Kantoō Tachi to Flat Daoshi

Examining the excavated swords and blades from the Asuka Period, numerous kantoō tachi—ceremonial large blades with a ring-shaped fitting (kantoō) on the hilt—can be identified. This is a design that Japan adopted from designs actively produced in Baekje, Silla, Goguryeo, and other kingdoms.

The kantoō functioned as a symbol of power and was bestowed upon the clan leaders of the Yamato regime and immigrant-descended chieftains. The continental influence remains distinctly evident in the swords and blades transmitted to temples of the Asuka Period such as Hōryū-ji and Shitennō-ji.

Sword and Blade Standards of Asuka to Nara Seen in the Shōsōin Treasures

The technological accumulation of the Asuka Period culminated in the Shōsōin Treasures of the Nara Period. The Shōsōin houses not only swords and blades imported from Tang but also straight blades manufactured in Japan, which are valuable materials demonstrating the level of Japan's metalworking technology during the Asuka to Nara periods.

Many of the swords and blades in the Shōsōin are elaborate, with lacquer, wood, leather, and metal decoration applied to the hilt and scabbard, and they have a character more of "ceremonial objects and gifts" than "implements for actual combat." This demonstrates that the "import" of the Asuka Period was not merely the adoption of weapons technology, but also the influx of crafted works with cultural and political significance.

Impact of Technological Imports of the Asuka Period on Subsequent Eras

Bridge to Tatara Smelting

The iron refining technology introduced from the continent during the Asuka and Nara periods subsequently transformed and developed into Japan's unique tatara smelting. The characteristic feature of tatara is tamahagane, obtained by reducing Japan's sand iron (magnetite-type) at low temperature over an extended period.

Tamahagane is a heterogeneous steel block in which sections with different carbon content coexist, and this heterogeneity itself gave birth to the Japanese sword's unique technique of "combining outer and inner steel" through repeated forging. It can be said that the result of "referring to continental refining techniques while evolving in a different direction" produced the unique sword culture of the Japanese sword.

Settlement of Immigrant-Descended Craftsman Communities

The blacksmiths who came from Baekje and their descendants settled in various parts of Japan as "katanabe" and "kajibe," served local clans and nobility, and transmitted their techniques. The existence of these craftsman communities formed the foundation for sword and blade production in the Nara and Heian periods and created a long chain of technique that would eventually lead to the Kamakura Period, the golden age of the Japanese sword.

Conclusion—The Significance of the Asuka Period's "Sword and Blade Import Period"

The Asuka Period is positioned as an "era of import and assimilation" in the history of the Japanese sword. Under the Suiko court's active foreign relations policy, steel refining techniques, tempering techniques, and sword and blade designs that flowed in through Sui and Baekje as primary channels significantly elevated the blacksmithing techniques of the Japanese archipelago. Tang-era technology was formally adopted through the missions to Tang from the Nara Period onward.

What is important is that Japan did not merely imitate these techniques, but rather transformed and made them uniquely their own to suit Japan's geographical conditions (the type of sand iron, climate, and forest resources). It is not an overstatement to say that the acceptance of techniques through Sui and Baekje during the Asuka Period, along with the "power to learn," laid the foundation for the later "unique and unparalleled sword culture of the Japanese sword."