Swords and Continental Iron Technology in the Asuka Period: How Metalworking from the Korean Peninsula and China Transformed Weaponry in Ancient Japan

Iron Culture in the Asuka Period——Continental Technology Transfer to the Archipelago

The Asuka period (592–710 CE) was an era in which Wa experienced rapid civilizational transformation through active exchange with China and the Korean Peninsula. Alongside cultural elements such as Buddhism, Chinese characters, and Confucianism, large-scale transfers of practical technology also occurred. Among these, the propagation of iron-working and blacksmithing technology represented one of the most crucial technological transfers, directly connected to weapons manufacturing.

Migrant technician groups from the continent (tōraijin) are documented in official histories such as the Nihon Shoki and Shoku Nihon Gi. Craftspeople known as the "Nishigori" and "Kanuchihe" clans, who arrived from Baekje, Goguryeo, and Silla between the 5th and 6th centuries, settled primarily in the Kinai region (present-day Osaka, Nara, and Hyogo) and established centers for iron goods production.

Japan possessed indigenous iron-working technology prior to the arrival of continental techniques during the Asuka period. During the Kofun period (3rd–7th centuries), a production system was established in which iron materials were imported from the continent and processed domestically, producing weapons, agricultural tools, and implements. However, iron-working technology at this stage did not match the high standards of the continent. The influx of continental technology during the Asuka period is believed to have sparked a qualitative leap.

Swords from the Asuka Period as Seen in Kofun Burial Goods

Swords unearthed from kofun (burial mounds) spanning the late Kofun period (6th century) through the Asuka period exhibit traces of technological changes that would lead to later nihontō.

Dominance of chokutō (straight blades): Asuka-period swords were fundamentally chokutō, and the distinctive curved form characteristic of Japanese swords had not yet been established. The blades were either single-edged or double-edged, following continental styles in which the angle between handle and blade approximated a straight line.

Gold and silver zōgan decoration: Some Asuka-period burial swords display elaborate ornamentation with gold and silver zōgan (metal inlay) on the handle and scabbard. This represents a direct import of continental weapon decoration styles, and scholars have noted parallels with burial swords of Baekje and Goguryeo royalty and nobility. The gilt-bronze-mounted large sword (ōtachi) excavated from the Fujinoki Kofun in Nara Prefecture (late 6th century) is recognized as a representative example.

Keitō and kantō tachi: Sword forms of the Asuka–Nara periods include the "keitō no tachi" (pointed-pommel tachi) and "kantō no tachi" (ring-pommel tachi). The keitō no tachi had a pointed, jade-disk-shaped pommel (tsukagashira), while the kantō no tachi featured a ring-shaped pommel. Both derive from large-sword styles of the Korean Peninsula and China, and were used by the elite power class in Asuka-period Japan.

Blacksmithing Techniques from Baekje and Goguryeo

During the early 7th century, the Korean Peninsula was dominated by the "Three Kingdoms" period, with Baekje, Goguryeo, and Silla in a three-way standoff and mutual conflict. This political instability provided the backdrop for many technicians and intellectuals to relocate to Japan.

The arrival of large numbers of Baekje people in Japan during Baekje's fall (660 CE) is known in connection with the "Baekje Relief Campaign (Battle of Baekgang, 663 CE)." Sword and iron-working craftspeople were included in this wave and settled primarily in Yamato, Kawachi, and Settsu (present-day Nara, Osaka, and Hyogo).

Migration from Goguryeo (which fell in 668 CE) followed a similar pattern. The place-name "Koma" (高麗) remaining in present-day Saitama and Kanagawa prefectures indicates settlements of Goguryeo-origin migrants from this period. Blacksmithing specialists were included in this population and formed the foundation for ancient iron-goods production in the Kantō region.

Among the techniques introduced by migrant blacksmiths, particularly important was iron-sand smelting technology approximating tatara iron-making. The Japanese archipelago possessed abundant iron-sand (satetsu) deposits, with the Chūgoku region (Izumo, Hōki, Mimasaka) being representative. The combination of these deposits with migrant technology is believed to have laid the technical foundation for later "tatara iron-making" and "tamahagane" (jewel steel) production.

The Shōsōin and Sword Materials from the Asuka and Nara Periods

The Shōsōin (正倉院) repository, affiliated with Tōdai-ji Temple in Nara, is internationally recognized as a facility housing imperial treasures from the Nara period (710–794 CE). Among its holdings are swords and weapons from the Asuka through Nara periods, providing invaluable materials for directly observing the influence of continental imported techniques.

Swords in the Shōsōin's collection such as the "kurozukuri no tachi" and "kingin sō no kara no tachi" represent chokutō forms strongly reflecting Tang (Chinese) styles. The blades are straight and uncurved, while handles and scabbards with gold and silver ornamentation approximate Tang treasure-sword styles. These swords demonstrate that Japan from the Asuka through Nara periods actively adopted continental sword styles.

Simultaneously, the Shōsōin also contains iron materials from the Korean Peninsula and swords believed to have been manufactured by migrant craftspeople, making it equally important as material evidence of improved production technology within the archipelago.

From the Asuka Period to Heian tachi——The Transition from Straight to Curved Blades

The transition from chokutō of the Asuka–Nara periods to the curved tachi established in the Heian period represents the most significant morphological change in the history of the Japanese sword.

Multiple theories explain why Asuka chokutō began curving in the early Heian period—including the spread of mounted-combat tactics, evolution of forging techniques, and refinement of materials (tamahagane)—but it is certain that the acceptance of continental technology during the Asuka period provided the technical foundation for this transformation.

As migrant blacksmiths settled in the Japanese archipelago and their techniques fused with those of indigenous craftspeople, distinctive iron-smelting and forging technologies developed. The roughly one-hundred-year period from the Nara through early Heian era represents a transitional phase of this fusion and independent evolution. The "Japanese sword" (nihontō) style established from the mid-Heian period onward is a product that, while grounded in continental-origin technology, evolved through Japan's unique climate, materials, and tactical requirements.

Understanding Asuka-period swords provides a starting point for exploring from a technical-historical perspective the answer to the question "Why did the Japanese sword assume that form?"