The Johei-Tengyo Rebellion (939-941) and Japanese Swords: How the Uprisings of Masakado and Sumitomo Shaped Sword Culture

The Shōhei-Tengyo Rebellion—The Turning Point of Warrior Ascendance Erupting Simultaneously East and West

The "Shōhei-Tengyo Rebellion (承平天慶の乱)" was a collective term for two simultaneous uprisings that occurred in both eastern and western Japan during 939–941 in the mid-Heian period.

The Hiraoka/Taira no Masakado Rebellion in the Eastern Provinces (939–940): An incident in which Taira no Masakado, a warrior who ruled the Bandō (Kantō) region, escalated his conflict with provincial governors (local officials) of the eastern provinces into a full-scale rebellion, declaring himself the "New Emperor (shinnou)" and establishing an independent kingdom. He was defeated by Fujiwara no Hidesatō and Taira no Sadamori.

The Fujiwara no Sumitomo Rebellion in the Western Provinces (939–941): A rebellion in which Fujiwara no Sumitomo, a former court official who commanded pirate groups in the Seto Inland Sea, attacked the provincial seats of the western provinces. The rebellion was suppressed by Ono no Yoshiko and Minamoto no Tsune-ki.

These two rebellions represent an extremely significant turning point in the history of the Japanese sword—namely, the era of warrior ascendance, the process by which swords transitioned from ceremonial objects of the nobility to the central practical weapons of samurai.

The Form of Swords at That Time—Late jōkototō to the Early Period of kotō

Around 939, when the Shōhei-Tengyo Rebellion erupted, the era was a transitional period from "jōkototō (上古刀)" to "kotō (古刀)" in the historical periodization of Japanese swords.

The Form of jōkototō (Nara through Early Heian)

jōkototō were swords from before the Nara period through the early Heian period, with the following characteristics:

chokutō (straight blades): Blades with little or no curvature—a linear form. They were strongly influenced by continental (Korean Peninsula and Chinese) sword culture.

Double-edged or single-edged: Early straight blades existed as both double-edged (ken) and single-edged (katana).

Diversity of form: warabi-te-tō, ke-nuki-gata-tachi, jōkototō, and other varied forms before the later "tachi" coexisted.

Swords in the Mid-Heian Period (Era of the Shōhei-Tengyo Rebellion)

The era of rebellion (early 10th century) was a transitional period in which gentle curvature began to develop in the blade. Swords of this period had the following characteristics:

The dawn of koshi-zori (waist curvature): Gentle curvature was beginning to appear in the koshi (root) section of the blade. This was the precursor to the typical "koshi-zori" of later "tachi".

Slender form: Swords of the early to mid-Heian period were generally slender, differing from the more robust form of the later Kamakura period.

The beginning of practical change: This was an accelerating period of transition from ceremonial swords to practical weapons. Large-scale armed conflicts such as the Masakado and Sumitomo rebellions created strong demands for swords with practical durability and cutting ability.

The Taira no Masakado Rebellion and Eastern Province Sword Culture

The "Warrior Culture" of the Bandō Samurai

Taira no Masakado was the chief of a warrior group based in Bandō (modern-day Kantō). In Masakado's era, eastern warriors had already been establishing a culture as a "warrior group wielding horse, bow, and sword."

Bow primary, sword secondary: The primary weapon of eastern samurai at this time was the bow and arrow. Combat on horseback with the bow was the main form of battle, while the sword (tachi) held a supplementary position in close combat and melee.

However, this combination of "bow + sword" directly led to later Kamakura warrior culture. The Masakado rebellion played a historical role in forming and strengthening warrior groups in the eastern provinces, becoming the foundation for the unique sword culture of the eastern provinces (leading to the lineages of the Sōshū tradition and Edo sword smiths).

The Swords Masakado Used

Detailed records do not survive of the specific swords that Taira no Masakado actually used, but as an eastern samurai of the early 10th century, the tachi he wore is presumed to have been of late jōkototō to early kotō form.

Legendary swords attributed to Masakado (such as those said to be dedicated to shrines throughout the country as "Masakado's tachi") are, upon actual authentication, mostly works from the Edo period and later, and no swords actually used by Masakado are confirmed to survive.

The Masakado Mound and Sword Reverence

After Masakado's defeat, his head was displayed. His head mound still remains in Ōtemachi, Tokyo today (the Masakado Mound). Masakado came to be feared in later ages as an "onryō (vengeful spirit)," and spiritual connections with swords were spoken of. At the Masakado Mound, memorial rituals have been regularly held, and the dedication of swords has been a traditional practice.

The Fujiwara no Sumitomo Rebellion and Western Province and Maritime Sword Culture

Seto Inland Sea Pirates and Swords

Fujiwara no Sumitomo was originally a court official (deputy provincial governor) but became the leader of a pirate group in the Seto Inland Sea.

Weapons that appear in contemporary records of pirate forces included bows, swords, and spears. In particular, in naval warfare on the Seto Inland Sea, swords played an important role in boarding (bringing ships into contact with each other) combat.

Western province sword-smithing regions: The western provinces (Ehime, Kōchi, Fukuoka, etc.) where the Sumitomo rebellion took place later developed into many sword-smithing centers. Bizen (modern-day Okayama) already had sword smiths active in this era, and it is presumed that demand for swords increased during the turmoil surrounding the Sumitomo rebellion.

The Indirect Impact of the Sumitomo Rebellion on the Sword Industry

After the Sumitomo rebellion was suppressed, warrior groups in the western provinces accumulated practical experience, and their demands on swords became more practically sophisticated. This demand is considered one of the background factors in the flourishing of Bizen sword smiths from the late Heian through Kamakura periods.

The Long-term Impact of the Shōhei-Tengyo Rebellion on the History of the Japanese Sword

Warriors Transitioning from "Military Force of the Nobility" to "Independent Warriors"

Before the Shōhei-Tengyo Rebellion, warriors were merely "hired military force for the court." However, when powerful warriors like Masakado and Sumitomo actually rebelled against the court, awareness spread that "warriors, if left unchecked, could become a dangerous independent force."

Ironically, this led to the "rise in the value and status of warriors," becoming a turning point in which warrior sword culture became socially valued.

The Strengthening of Eastern Province Warrior Groups and "Bandō Swords"

After the Masakado rebellion was suppressed, a self-conscious group of warriors was formed in the eastern provinces (Bandō). This eastern warrior group later became the foundation for Minamoto no Yoritomo and led to the establishment of the Kamakura shogunate.

The sword culture of the eastern provinces made a major contribution to the technological development of Japanese swords in the late Heian through Kamakura periods. The flowering of the Sōshū tradition (a major school of Kamakura-period swords) in the eastern provinces (Kamakura) was not unrelated to the historical circumstance that the Shōhei-Tengyo Rebellion strengthened the eastern province warrior groups.

Acceleration of the Geographical Dispersal of Sword Smiths

The turmoil of the Shōhei-Tengyo Rebellion likely accelerated the dispersal of sword smiths from the center (Kyoto and Nara) to the provinces. Warrior groups in the eastern and western provinces began to protect and support sword smiths in their respective regions, leading to the emergence of regional sword cultures.

Conclusion—The Masakado and Sumitomo Rebellions Defined "The Warrior's Sword"

The Shōhei-Tengyo Rebellion did not bring direct technological innovation to the Japanese sword. However, this rebellion was a historical event that fundamentally changed "the social meaning of a warrior carrying a sword."

The fact that Masakado proclaimed himself New Emperor and attempted to establish an independent regime in the eastern provinces; the fact that Sumitomo rebelled against court control—these facts implanted in Japanese society the recognition that "a warrior's sword is also a symbol of power."

This recognition deepened through the formation of samurai society over the approximately 250 years leading to the establishment of the Kamakura shogunate (1185), becoming one of the remote causes for Japanese swords to come to be revered culturally and spiritually as "the soul of the warrior."