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

Iron Culture of the Asuka Period——Transmission of Continental Technology to the Archipelago

The Asuka period (592–710) was an era in which Japan underwent rapid civilizational transformation through active exchange with China and the Korean Peninsula. Alongside cultural elements such as Buddhism, Chinese characters, and Confucianism, large-scale transfer of practical technologies also advanced. Among these, the transmission of iron tools and blacksmithing techniques was one of the most important technological transfers, directly connected to weapons manufacturing.

Records remain in official histories such as the Nihon Shoki and Shoku Nihongi regarding craftsman groups from the continent (tôraijin). From the fifth to sixth centuries, occupational groups called the Nishigori and Kanuchibe who came from Baekje, Goguryeo, and Silla settled primarily in the Kii region (present-day Osaka, Nara, and Hyogo), forming centers of iron tool manufacturing.

Nevertheless, Japan in the Asuka period possessed indigenous iron tool manufacturing techniques even before the influx of continental technology. 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, the technology at this stage did not reach the high standards of the continent, and it is believed that a qualitative leap occurred with the influx of continental techniques during the Asuka period.

Blades from Kofun Burial Goods: Swords of the Early Asuka Period

Swords excavated from kofun (burial mounds) from the late Kofun period (6th century) through the Asuka period show traces of technological changes leading to later Japanese swords.

• Straight blades (choktou) as mainstream: The blades of the Asuka period were fundamentally straight, and the characteristic curved form of Japanese swords had not yet been established. The blade was single- or double-edged, and it followed the continental style in which the angle between hilt and blade was nearly straight.
• Gold and silver inlay decoration: Some burial blades display lavish decoration with gold and silver inlay applied to the hilt and scabbard. This was a direct import of continental weapon-decoration styles, and similarities to burial blades of Baekje and Goguryeo royalty and nobility have been noted. The gold and copper-decorated large blade excavated from the Fujinoki Kofun in Nara Prefecture (late 6th century) is known as a representative example.
• Keito-no-tachi and kanto-no-tachi: The sword forms of the Asuka to Nara periods include the "keito-no-tachi" and "kanto-no-tachi." The keito-no-tachi has a pommel (tsukagashira) with a pointed keito (jade-disc) shape, while the kanto-no-tachi has a pommel with a ring (wa) shape. Both derive from large sword styles of the Korean Peninsula and China, and were used by the powerful elite of Asuka-period Japan.

Blacksmithing Techniques from Baekje and Goguryeo

In the first half of the seventh century, the Korean Peninsula saw the "Three Kingdoms period" with Baekje, Goguryeo, and Silla in tripartite confrontation and mutual conflict. This political instability was the background that prompted many technicians and intellectuals to migrate to Japan.

The mass migration of Baekje people accompanying the fall of Baekje (660 CE) is well known in connection with the "Baekje Relief Campaign (Battle of Baekgang, 663 CE)." Blade and iron tool craftsmen were included in this wave and settled primarily in Yamato, Kawachi, and Settsu (present-day Nara, Osaka, and Hyogo).

Migrants from Goguryeo (destroyed 668 CE) were similar, and place names such as "Koma" remaining in present-day Saitama and Kanagawa prefectures indicate settlement areas of Goguryeo-origin migrants from this period. Blacksmithing technicians were included in this group and formed the foundation for ancient iron tool manufacturing in the Kanto region.

Among the techniques brought by immigrant-origin blacksmith craftsmen, iron sand refining techniques close to tatara smelting were particularly important. The Japanese archipelago possessed abundant sources of iron sand centered on regions such as Izumo, Hōki, and Mimasaka in the Chugoku region, and through combination with continental techniques, the technical foundation for later "tatara smelting" and "tamahagane" is believed to have been established.

The Shosoin and Blade Records from the Asuka and Nara Periods

The Shosoin, affiliated with Todai-ji Temple in Nara, is world-renowned as a repository for imperial treasures from the Nara period (710–794). Among those treasures are blades and weapons from the Asuka through Nara periods, serving as invaluable materials for directly observing the influence of continental techniques.

Blades preserved at the Shosoin such as the "Kurozukuri-no-tachi" and "Kinginso-no-kara-no-tachi" are straight-blade forms strongly reflecting Tang (Chinese) styles. The blade has a straight form without curvature, and the hilt and scabbard adorned with gold and silver are close to Tang treasure sword styles. These demonstrate that Asuka- through Nara-period Japan actively adopted continental sword styles.

At the same time, the Shosoin contains iron materials of Korean Peninsula origin and blades presumed to have been manufactured by immigrant-origin craftsmen, and these are regarded as important materials indicating the elevation of production technology levels within the archipelago.

From Asuka Period to Heian Tachi——Transition from Straight to Curved Blades

The transition from straight blades of the Asuka and Nara periods to the curved tachi established in the Heian period represents the most important morphological change in the history of the Japanese sword.

Regarding the causes of the Asuka-period straight blade curving in the early Heian period, there are multiple theories including the spread of mounted warfare tactics, evolution of forging techniques, and refinement of materials (tamahagane); however, it is certain that the adoption of continental techniques in the Asuka period formed the technical foundation for this change.

Immigrant-origin blacksmith craftsmen settled in the Japanese archipelago, and as their techniques fused with those of indigenous craftsmen, unique smelting and forging techniques developed. The approximately hundred years from the Nara through early Heian period represents the transitional stage of this fusion and independent development. The "Japanese sword" style established after the mid-Heian period is a product that, while based on techniques of continental origin, evolved in response to Japan's unique climate, materials, and tactical requirements.

Understanding Asuka-period blades serves as a starting point for exploring from a technical-historical perspective the answer to the question: "Why did the Japanese sword take that form?"