上古刀（古墳〜奈良時代）

The Arrival of Continental Ironworking

During the Yayoi period (roughly the 3rd century BCE to the 3rd century CE), the technology of iron manufacture arrived in the Japanese archipelago from the Korean peninsula and the Chinese continent. The earliest iron objects were primarily agricultural and craft tools; swords and daggers are thought to have been introduced somewhat later. As the Kofun period (3rd–7th centuries) began, numerous straight swords and short blades appeared as burial goods in the great earthen tombs of regional chiefs, indicating that local swordsmithing skills were steadily advancing.

The swords of this era are collectively called jōkotō (ancient swords), a conventional term distinguishing them from the later Japanese sword (the curved tachi). As straight-bladed forms, they retain clear continuity with continental sword types. The standard form features a blade without curvature, with edge and spine running parallel. Swords are classified by pommel type: ring-pommel swords (kantō-tachi), diamond-pommel swords (keitō-tachi), single-phoenix-ring-pommel swords, and others.

Characteristics and Technology of Kofun-Period Swords

Swords excavated from kofun include both ceremonial burial pieces and functional weapons. Technical quality improved steadily over time, and metallurgical analysis has confirmed that quench-hardening technology had been introduced by around the 5th–6th centuries.

A landmark example is the gold-inlaid iron sword excavated from the Inariyama Kofun in Gyōda, Saitama. Its 115-character gold-inlay inscription records a date of 471 CE and provides critical historical evidence for the political power structures of the time. Finely crafted iron swords have also been recovered from elite burial sites across the country, and it is widely suggested that skilled swordmakers from the Korean peninsula who migrated to Japan in the 5th century substantially elevated local forging technology.

The Shichishito — the seven-branched sword preserved at Isonokami Shrine in Nara — is traditionally said to have been presented to the Yamato king by the kingdom of Baekje in the 4th century. Manufactured not as a functional weapon but as a ritual implement, this extraordinary object is among the most important artifacts documenting both the political relationship between Japan and the Korean peninsula in antiquity and the high level of metalworking skill of that era.

Shōsōin and Swords of the Asuka and Nara Periods

From the Asuka period (593–710) through the Nara period (710–794), sword culture underwent major transformation alongside the formation of the ritsuryo (imperial code) state. The imperial court's enthusiastic absorption of Tang Chinese culture produced elaborately decorated ceremonial swords with magnificent metalwork.

The Shōsōin repository at Tōdaiji Temple in Nara preserves swords associated with Emperor Shōmu. Works such as the Kingindenso Karatachi (gold-silver-inlaid Tang-style long sword) and the Kingindenso Katana — adorned with gold, silver, shell, and gemstones on hilt and scabbard — are internationally acclaimed as artworks representing the cultural pinnacle of the Nara court. While these blades retain the straight-sword form, their forging technique and blade geometry had reached a stage that formed a bridge to the Japanese sword of later centuries.

The Warabite-Tō and the Transition to Curved Blades

The transition from jōkotō (straight swords) to Japanese swords (curved tachi) was not sudden — it unfolded over approximately two centuries from the 8th to the 10th century. One sword type that served as a bridge in this transition was the warabite-tō (bracken-fern-hilt sword).

The warabite-tō was used by the Emishi, the indigenous people of northern Japan (Mutsu and Dewa provinces, encompassing present-day Tohoku), and is characterized by a distinctive pommel that curls inward like the emerging frond of a bracken fern. Specimens have been excavated from sites throughout the Tohoku region, including the vicinity of present-day Sendai. Academically important as a transitional form between the straight and curved sword, the warabite-tō raises the intriguing possibility that Tohoku sword culture contributed to the birth of the Japanese sword. The incipient curvature visible in warabite-tō is a revolutionary characteristic directly anticipating the curved form of the later Japanese sword.

The Modern Significance of Jōkotō

Jōkotō occupy a specialized category that rarely appears in the modern Japanese sword collector market; their study belongs at the intersection of archaeology, cultural property science, and sword history. Nevertheless, knowledge of jōkotō is indispensable for a deeper understanding of the historical miracle that was the birth of the Japanese sword.

Why did the Japanese sword come to have its distinctive form and method of manufacture? Part of the answer lies in the jōkotō period itself — in the overlapping forces of continental technology transfer, trial and error by craftspeople across the archipelago, the demands of actual combat, and the aesthetic vision of the imperial court. Through studying sword history, we can rediscover something of the sense of cultural continuity and transformative wonder that the samurai must have felt when they encountered the ancient treasures of Shōsōin.