Iron Swords of the Yayoi Period and the Origins of Japanese Sword Culture——The Transmission of Iron Tools from the Continent and the Prehistory of the Japanese Sword

Before the Japanese Sword Era

The curved single-edged long sword known today as the "Japanese sword" is said to have been established in the mid-Heian period (late 9th–10th centuries). However, even before that, the Japanese archipelago possessed its own blade culture. Tracing its origins leads to iron tool culture that arrived from the continent during the Yayoi period. The start date of the Yayoi period was traditionally said to be "around the 3rd century BC," but recent research based on radiocarbon dating suggests the possibility it extends back to around the 10th century BC, and academic discussion continues. However, there is agreement among all theories that the full-scale introduction and spread of iron tools occurred from the mid-Yayoi period onward.

Iron Tool Introduction in the Yayoi Period

Before the Yayoi period, during the preceding Jomon period, blades used in the Japanese archipelago were primarily stone tools, either struck or polished. With the arrival of the Yayoi period, iron tools from the Korean Peninsula and mainland China began to be introduced. The oldest excavated examples are concentrated in the northern Kyushu region, and the Korean Peninsula's southern coast is believed to have been the primary transmission route.

Early iron blades took the form of "chokutou" (straight swords) or "ken" (swords). These were strongly influenced by Chinese sword culture (Han dynasty short and long swords) and were predominantly double-edged swords. Iron tools served both practical purposes as agricultural implements and symbolic roles as expressions of authority and ritual.

Coexistence with Yayoi Bronze Swords

A significant point to note is that during the Yayoi period, iron and bronze tools were used in parallel. In northern Kyushu, bronze "douken" (bronze swords) and "douhou" (bronze spears) served ritual functions, while iron blades are interpreted as having been prioritized for actual warfare and practical use.

Additionally, the "hirogata douhou" (wide-form bronze spears) distributed primarily in northern Kyushu eventually exceeded 1 meter in length by the late Yayoi period, making them impossible to carry or use in actual combat. This is regarded as evidence that they completely transformed from weapons into ritual implements that demonstrated divine authority in group ceremonial contexts. This shift is noteworthy as a typical example of how blades changed meaning from the "martial" to the "sacred."

From famous Yayoi period archaeological sites in Fukuoka Prefecture (such as the Sugu Okamoto site in Kasuga City), iron sword fragments imported from the continent have been unearthed alongside iron implements that may have been manufactured within the archipelago. The iron tool manufacturing technology of this period was imported from the continent, and iron smelting (smelting furnaces) had not yet become established within the archipelago.

What symbolizes the scale of these accumulated bronze ritual objects are the Arajingani site and Kamogani site excavated in Shimane Prefecture. The excavation findings from both sites are as follows:

These excavation findings reveal that the Izumo region possessed powerful religious customs of systematically "burying" and depositing Yayoi ritual implements.

Transition to the Kofun Period and Transformation of Iron Swords

As the transition occurred from the Yayoi period to the Kofun period (mid-3rd century–around 7th century), the quantity of excavated iron swords and iron blades increased dramatically. An important transformation took place during this period——the shape of blades diversified, and a clear distinction emerged between single-edged "katana" (swords) and double-edged "tsurigi" (swords).

Iron swords unearthed as burial goods from kofun (mounded tombs) served a strong function as prestige items symbolizing the authority and status of the deceased. Representative artifacts that demonstrate the intimate connection between rulers of this period and iron weapons include:

• A "daitou" (great sword) with silver-inlaid inscription unearthed from Edafunayama kofun in Kumamoto (late 5th century)
• A "tetsutsurugi" (iron sword) with gold-inlaid inscription unearthed from Inari kofun in Saitama Prefecture

The Emergence of "tatara Smelting" and Domestic Production

Large-scale indigenous iron production in the Japanese archipelago is thought to have begun around the 5th–6th centuries. The prototype of "tatara smelting" was introduced from the Korean Peninsula, and smelting furnaces using iron sand as raw material gradually spread throughout various regions. This inception of domestically produced iron would form the material foundation for Japan's distinctive sword culture.

By the Nara period (8th century), under the ritsuryo system of imperial governance, sword manufacturing and possession came under certain regulations, and "katanakou" (swordsmiths) became institutionally recognized as a profession. At this stage, straight swords remained the dominant form, and the curves characteristic of modern Japanese swords had not yet emerged.

From Yayoi Iron Tools to the Japanese Sword——A Thousand-Year Journey

From the introduction of iron tools in the Yayoi period to the establishment of the curved "Japanese sword" in the mid-Heian period, approximately 1,000 years elapsed. During this span, the straight-sword culture derived from the continent gradually merged with elements unique to the Japanese archipelago, giving rise to a distinctive sword culture without parallel anywhere in the world.

• Material (iron sand)
• Technology (tatara smelting and fold forging)
• Purpose (mounted warfare)

In the works that modern sword collectors appreciate as "Japanese swords," the foundational undercurrent carries the imprint of the first encounter Yayoi people had with iron as a material received from the continent. When discussing the history of the Japanese sword, the iron sword culture of the Yayoi period stands as its essential "prehistory."

Implications for Sword Collectors——The Meaning of Understanding "Prehistory"

Direct collection of iron implements from the Yayoi and Kofun periods is difficult for most private collectors, but knowledge of this prehistory significantly deepens the appreciation of Japanese swords. The characteristics of tamahagane born from tatara smelting——uneven carbon distribution that becomes homogenized through fold forging, creating the distinctive jihada and hamon——is the product of a long history beginning with iron sand, a material unique to the Japanese archipelago. Furthermore, knowing that iron swords which became widespread from the mid-Yayoi period onward were straight swords (chokutou), and that the distinctive curves of modern Japanese swords first emerged in response to changes in mounted warfare tactics during the mid-Heian period, allows one to realize that the blade in one's hand is not merely a craft object, but a convergence point of materials, techniques, and culture spanning thousands of years. Since research into the Yayoi period continues to advance, the "prehistory" of the Japanese sword remains a living field that will continue to be updated.

Related Column: Kogarasumaru——A Masterpiece of Early Heian Ancient Swords