Iron Swords of the Yayoi Period and the Origins of Sword Culture — The Arrival of Iron Implements from the Continent and the Prehistory of the Nihontō

The World of Swords Before the Nihontō

The curved, single-edged longsword known today as the nihontō is considered to have taken shape in the mid-Heian period (late 9th to 10th century). However, even before that, a distinctive blade culture existed on the Japanese archipelago. Tracing its origins leads back to the iron implement culture that arrived from the continent during the Yayoi period. The start date of the Yayoi period has traditionally been placed at "around the 3rd century BCE," but research based on recent radiocarbon dating has suggested the possibility of going back to around the 10th century BCE, and debate continues in academic circles. Note that all theories agree that the full-scale arrival and spread of iron implements occurred from the Middle Yayoi period onward.

The Arrival of Iron Implements in the Yayoi Period

In the Jōmon period preceding the Yayoi, the bladed implements used on the Japanese archipelago were primarily chipped and polished stone tools. With the advent of the Yayoi period, iron implements from the Korean peninsula and the Chinese continent began to be introduced. The oldest excavated examples are concentrated in the northern Kyushu region, and exchange with the southern part of the Korean peninsula is considered to have been the main route of transmission.

Early iron blades took the form of the straight-bladed chokutō or ken (tsurugi). These were strongly influenced by Chinese sword culture (Han-dynasty short swords and long swords), and double-edged swords were common. Iron implements as practical agricultural and craft tools and iron swords as symbols of authority and ritual spread in parallel.

Coexistence with Yayoi Bronze Swords

A noteworthy point is that iron implements and bronze implements were used in parallel during the Yayoi period. In the northern Kyushu region, bronze dōken (bronze swords) and dōhoko (bronze spears) served a ritual role, while iron blades were given priority for actual combat and practical use.

Moreover, the hirogata-dōhoko (wide-type bronze spears) distributed mainly in northern Kyushu grew to more than 1 meter in total length by the Late Yayoi period, reaching a size at which carrying and using them in actual combat was impossible. This is seen as evidence that they had completely transformed from functioning as weapons into ritual implements to demonstrate divine authority at communal ceremonies, and they attract attention as a typical example of blades shifting in meaning from "martial" to "sacred."

From well-known Yayoi-period sites in Fukuoka Prefecture (such as the Sugu Okamoto site in Kasuga City), fragments of iron swords imported from the continent have been excavated alongside iron objects that may have been produced within the Japanese archipelago. The iron-working techniques of this period were imported from the continent, and iron smelting (blast furnaces) within the archipelago had not yet been established.

Symbolic of the scale of this accumulation of bronze ritual implements are the Kōjindani site and the Kamo Iwakura site, excavated in Shimane Prefecture. The excavation details of the two sites are as follows.

These excavation patterns indicate that in the Izumo region there was a strong religious custom of concentrating Yayoi ritual implements and "burying" them together.

The Transition to the Kofun Period and the Transformation of Iron Swords

As the Yayoi period transitioned into the Kofun period (approximately the second half of the 3rd century to around the 7th century), the volume of iron swords and iron blades excavated increased dramatically. An important change occurred during this period — blade shapes diversified, and the distinction in use between the single-edged katana and the double-edged tsurugi became clearly defined.

Iron swords excavated as burial goods from kofun (burial mounds) were strongly characterized as prestige objects demonstrating the authority and status of the interred. The following are cited as representative artifacts that illustrate the close relationship between rulers and iron weapons during this period.

• The silver-inlaid inscribed tachi excavated from the Eta Funayama kofun (late 5th century) in Kumamoto Prefecture
• The gold-inlaid inscribed iron sword excavated from the Inariyama kofun in Saitama Prefecture

The Emergence of "Tatara Smelting" and Domestic Production

Full-scale domestic iron production on the Japanese archipelago is believed to have begun around the 5th to 6th century. A smelting method that became the prototype of tatara smelting was introduced from the Korean peninsula, and smelting furnaces using iron sand as raw material began to spread throughout the country. This start of domestic iron production would go on to form the material foundation for Japan's distinctive sword culture.

In the Nara period (8th century), the manufacture and possession of swords came under certain regulations under the ritsuryō system, and the occupation of tōkō (swordsmith) came to be institutionally recognized. At this stage, the straight chokutō remained the mainstream blade form, and the curvature seen in the modern nihontō had not yet emerged.

From Yayoi Iron Implements to the Nihontō — A Journey of Approximately 1,000 Years

From the arrival of iron implements in the Yayoi period to the establishment of the curved-bladed nihontō in the mid-Heian period, a full approximately 1,000 years passed. During this time, the continental tradition of the chokutō fused with elements unique to the Japanese archipelago, and a distinctive sword culture without parallel in the world was cultivated.

• Material (iron sand)
• Technique (tatara smelting and orikaeshi tanren)
• Use (mounted combat)

Underlying the works that modern sword collectors admire as "nihontō" is the imprint of the Yayoi people's first contact with iron as a material received from the continent. When telling the history of the nihontō, the iron sword culture of the Yayoi period is positioned as its indispensable "prehistory."

Implications for Sword Collectors — The Meaning of Knowing the "Prehistory"

While directly collecting Yayoi- and Kofun-period iron implements is difficult for ordinary collectors, knowledge of this prehistory greatly deepens the experience of appreciating the nihontō. The properties of tamahagane produced through tatara smelting — in which non-uniform carbon distribution is homogenized through orikaeshi tanren (folding), giving rise to the distinctive jihada and hamon — are a product of a long history beginning with iron sand, a material unique to the Japanese archipelago. Furthermore, knowing that the iron swords that spread from the Middle Yayoi period onward were chokutō, and that the sori distinctive to the modern nihontō first emerged in response to changes in mounted cavalry tactics in the mid-Heian period, allows one to feel that the single sword in hand is not merely a craft object but a nexus of materials, techniques, and culture spanning thousands of years. As research into the Yayoi period continues to advance, the "prehistory" of the nihontō is also a living field that continues to be updated.

Related column: Kogarasu-maru — The Finest Masterpiece of Early Heian kotō