Swords of the Asuka Period

The Asuka period (593–710) was a pivotal moment in history when the Yamato court underwent transformation into a centralized ritsuryo state, and this political upheaval profoundly influenced Japanese sword culture. Paralleling the active reception of continental civilization——Buddhism, Chinese writing, and the ritsuryo system——metalworking technology from the Korean peninsula and Chinese mainland flowed into Japan through toraijin (immigrant craftsmen and technicians), fundamentally altering the technical foundations of sword production.

The swords of Japan before the Asuka period belonged to the straight-sword (chokutō) tradition from the Yayoi and Kofun periods. Iron straight swords, first brought from the Chinese mainland and elsewhere in the late Yayoi period, formed the military core of the Yamato polity in the Kofun period, but metalworking and forging technology at this stage remained heavily dependent on knowledge brought by toraijin. With the advent of the Asuka period, this technology began to take root and develop within Japan, and the prototype of Japan's distinctive "tatara" iron-smelting method began to be attempted in various regions.

Surviving swords from the Asuka period include the Heishi Shōrin-ken and the Shichisei-ken, both National Treasures handed down at Shitennō-ji (Osaka). Both are straight swords traditionally said to have been worn by Prince Shōtoku. Together with the Nara-period swords preserved in the Shōsōin (Nara), they show that continental-style straight swords were used in Japan from the Asuka through the Nara periods. The Shichishitō (Seven-Branched Sword) of Isonokami Shrine (Tenri, Nara Prefecture) is an iron sword said to have been made in Baekje in the fourth century and presented to the king of Wa; it attests to Japanese–Korean exchange before the Asuka period.

The Jinshin War (672), the greatest civil disturbance of the Asuka period, was a succession dispute fought between Prince Ōtomo (son of Emperor Tenji) and Emperor Tenmu (then known as Prince Ōama). Emperor Tenmu, victorious in the Jinshin War, hastened the establishment of the ritsuryo system. In 686 (Shuchō 1), when the emperor fell ill, divination attributed the illness to a curse of the Kusanagi-no-Tsurugi, which had been kept at the palace, and the sword was returned to Atsuta Shrine (Nagoya).

From the late Asuka through the early Nara period, iron-smelting technology advanced dramatically. The nascent form of "tatara"——Japan's distinctive method of refining iron sand in furnaces——began to be confirmed, establishing the technical foundation that would enable the production of tamahagane (jewel-steel), the material of Japanese swords. The accumulation of this technology provided the fundamental condition that enabled the revolutionary evolution of Japanese swords in the late Heian period. The Asuka period thus occupies the position of the direct prehistory of Japanese swords, serving as the starting point for all development of Japanese sword culture.