November 21, 939.
Taira no Masakado led over a thousand soldiers to advance on the provincial government of Hitachi.
According to the “Shomonki,” the forces defending the Hitachi provincial government numbered 3,000. In terms of sheer numbers, the provincial side had the advantage.
The battle concluded with a victory for Masakado’s forces.
Fujiwara no Korechika, the governor of Hitachi, was captured, and Masakado seized the official seals symbolizing the provincial authority.
He then advanced his troops into Shimotsuke and Kozuke, declaring himself the “New Emperor” by December 19.
This was the Taira no Masakado Rebellion, which shook the imperial court’s control over the provinces.
Just over four years earlier, Masakado’s adversaries were the powerful Minamoto no Mamoru family of Hitachi and others connected to the same Kanmu Taira lineage.
From the battles of 935, the death of Taira no Kunika, fierce clashes with Taira no Yoshikane, legal disputes in Kyoto, pursuits by Taira no Sadamori, to interventions in the Musashi province conflicts, the strife surrounding Masakado expanded.
And then came 939.
Having fought through the internal clan conflicts of the Kanto region, Masakado finally seized the provincial government established by the imperial court through military force.
Why did Taira no Masakado go this far?
The origins lay in Hitachi province in the fifth year of the Shōhei era (935).
1. The Kanmu Taira Clan’s Expansion in the Kanto Region
Taira no Masakado belonged to the Kanmu Taira clan, descendants of Emperor Kanmu.
His grandfather was Taira no Takamochi. There are traditions that name his father as either Taira no Yoshimasa or Yoshimochi.
Masakado established his power base in the northern part of Shimousa Province, centered around Toyoda and Sashima districts. This area corresponds to the western part of present-day Ibaraki Prefecture, where the Kinu and Tone river systems spread.
Surrounding him were influential relatives like Taira no Kunika, Taira no Yoshikane, and Taira no Yoshimasa.
The Taira clan had deeply rooted themselves across the Kanto region, developing the land while forging relationships with local elites and provincial governors, each forming their own power bases.
Within the clan, bound by blood ties, there were competing interests over land, marriage, and local control.
Relations between Masakado and his uncles gradually deteriorated.
The “Shomonki,” which provides a detailed account of Taira no Masakado’s rebellion, lacks the opening section of the surviving text, leaving the full circumstances of the conflict’s origins unclear.
This rivalry escalated into a large-scale military clash in 935.
2. February 935—The Battle of Nomoto
February of the fifth year of the Shōhei era (935).
In Hitachi Province, Masakado clashed with the forces of Minamoto no Mamoru’s sons, Minamoto no Tasu, Minamoto no Taka, and Minamoto no Shigeru.
Minamoto no Mamoru was a powerful figure in western Hitachi, deeply connected to the Taira clan through marriage.
According to the “Shomonki,” Minamoto no Tasu and his brothers set up camp near Nomoto, lying in wait for Masakado.
Upon spotting the enemy forces, Masakado hesitated but, once the battle commenced, took the upwind position and unleashed a barrage of arrows.
Minamoto no Tasu’s forces crumbled.
Tasu, Taka, and Shigeru lost their lives in this series of battles.
On February 4th, Masakado continued his offensive, advancing into areas such as Nomoto, Ishida, Ogushi, and Toriki.
The Shomonki records that over 500 homes were burned in the three districts of Tsukuba, Makabe, and Niihari.
During this battle, Masakado’s uncle, Taira no Kunika, was also killed.
The death of Kunika, a prominent figure in the Taira clan, further intensified the conflict surrounding Masakado.
3. The Death of Taira no Kunika—Taira no Sadamori Returns to the East
Kunika had a son named Taira no Sadamori.
At the time of his father’s death, Sadamori was in Kyoto.
Upon learning of Kunika’s death, Sadamori returned to the eastern provinces.
He would later become known as the man who, alongside Fujiwara no Hidesato, defeated Masakado.
At that time, Sadamori also had a path to live as an official in Kyoto, so continuing a full-scale war with Masakado was not his sole objective.
Meanwhile, it was Taira no Yoshimasa who pressed on with the fight against Masakado.
On October 21st, 935 (Shohei 5).
Yoshimasa gathered troops and engaged Masakado at Kawamawari Village in Niihari District.
Masakado’s forces emerged victorious, and Yoshimasa was forced to retreat.
Yoshimasa sought assistance from Taira no Yoshikane.
Yoshikane was also an uncle of Masakado.
The conflict that began with battles against the Minamoto clan expanded into a full-scale feud between Masakado and the Taira clan.
4. June 936—Chasing Yoshikane’s Army to the Shimotsuke Provincial Government
On June 27th, 936 (Shohei 6).
Taira no Yoshikane joined forces with Yoshimasa and Sadamori to fight against Masakado.
The Shomonki notes that Yoshikane’s side had over a thousand soldiers.
Masakado defeated Yoshikane’s army.
Yoshikane and his allies retreated, fleeing to the Shimotsuke Provincial Government.
Masakado’s forces pursued them and laid siege to the government center.
The provincial government was the administrative hub where the provincial governor conducted affairs.
While cornering his enemies, Masakado left an escape route open for Yoshikane and his allies.
The Shomonki describes how Masakado believed that annihilating his kin would invite public condemnation.
At this time, Masakado had not yet succeeded in seizing control of the Shimotsuke provincial government itself.
Three years later, in 939.
The same Masakado would go on to seize the official seals from the provincial government.
5. October 936—Masakado Judged in Kyoto
The battles in the Kanto region reached the ears of the imperial court.
Minamoto no Mamoru, having lost his sons, lodged a complaint against Masakado with the court.
On October 17, 936 (Shōhei 6).
Masakado responded to the summons and traveled to Kyoto, where he was tried by the Kebiishi, the imperial police and judicial office.
At this time, Masakado was in a position where he had to comply with the court’s orders and face judgment in Kyoto.
On April 7, 937 (Shōhei 7).
Masakado was pardoned as part of a general amnesty accompanying Emperor Suzaku’s coming-of-age ceremony.
Masakado returned to the Kanto region.
However, the conflicts within his clan did not cease.
What awaited Masakado upon his return was a fierce battle with Taira no Yoshikane.
6. August 937—Masakado Suffers Consecutive Defeats
On August 6, 937 (Shōhei 7).
Taira no Yoshikane attacked Masakado near the Kokai crossing, located on the border between Hitachi and Shimousa provinces.
According to the “Shomonki,” Yoshikane’s army displayed images of their common ancestor, Prince Takamochi, and Masakado’s father, Yoshimasa, at the forefront.
It was a battle that prominently featured their shared lineage.
On this day, Masakado was unable to gather enough troops and was forced to retreat.
Yoshikane’s forces entered Masakado’s territory, setting fire to places like the Tokawa Imperial Stables in Kurusu-in, Toyoda District.
Masakado prepared for a counterattack.
On August 17.
He awaited Yoshikane’s forces again at the Horikoshi crossing in Shimoogata-go, Toyoda District.
The “Shomonki” records that Masakado increased his troops and gathered 370 spears in preparation for the battle.
However, on the day of the battle, Masakado suddenly suffered from “leg illness.”
As Yoshikane’s forces advanced, Masakado’s army crumbled and retreated once more.
Furthermore, Masakado’s wife and children were captured by Yoshikane’s side.
His wife, said to be Yoshikane’s daughter, later returned to Masakado with the help of her brothers.
In the summer of 937.
Masakado suffered significant military setbacks.
Nevertheless, his power did not collapse entirely.
7. The Night Raid on the Ishii Encampment
On December 14, 937 (Shōhei 7).
Yoshikane won over Koshibumaru, who had been serving Masakado.
He extracted information about the internal situation of the Ishii encampment from Koshibumaru and launched a night raid.
According to the “Shomonki,” Masakado had fewer than ten soldiers with him at the time.
Masakado himself took up a bow and faced Yoshikane’s forces.
They shot and killed Tajirari and others on Yoshikane’s side, repelling the night attack.
Since 935, the conflict had been marked by repeated assaults on the manor, arson, family abductions, and night raids.
Yoshikane eventually lost his power and died of illness in 939.
The long struggle between Masakado and the influential members of his clan reached a turning point.
However, Masakado’s battles themselves were moving onto a larger stage.
8. The Year 938—Pursuing Taira no Sadamori to Shinano
February 29, 938.
Taira no Sadamori left the Kanto region, intending to travel to Kyoto via the Tosan-do road.
Upon learning of this, Masakado pursued him.
The battlefield extended beyond the Kanto region, reaching as far as Shinano Province.
Near Kokubunji in Chiisagata District, Shinano Province, Masakado’s forces caught up with Sadamori, leading to a battle.
Sadamori managed to escape and reached Kyoto.
There, he appealed to the court about Masakado’s actions.
On February 12, 939, there were moves to summon Masakado under the auspices of the Grand Minister of State, Fujiwara no Tadahira.
It is said that Masakado, in his youth, went to Kyoto and served under Tadahira.
The clan conflict in the Kanto region was once again tied to Kyoto politics due to Sadamori’s journey to the capital.
9. From 938 to 939—The Conflict in Musashi Province
While Masakado was engaged in battles with the Taira clan, a significant conflict was also unfolding in Musashi Province.
Around 938, a dispute arose between the governor of Musashi Province, Koseo, and the assistant governor, Minamoto no Tsunemoto, and Musashi Takeshiba, the district governor of Adachi.
This was a conflict between the provincial officials and the powerful local district governors.
On March 3, 939, Masakado headed to Musashi Province to mediate.
Thanks to Masakado’s mediation, Koseo and Musashi Takeshiba reconciled, and a banquet was held.
During the banquet, Takeshiba’s forces surrounded Tsunemoto’s camp.
Fearing for his safety, Tsunemoto fled to Kyoto.
There, he accused Masakado and Koseo of plotting rebellion to the court.
Masakado responded to this.
On May 2, he submitted documents from the five provinces of Hitachi, Shimosa, Shimotsuke, Musashi, and Kozuke, reporting to Fujiwara no Tadahira that there was no rebellion.
Masakado’s explanation was accepted, and the court did not move to pursue him at that time.
In the spring of 939, Masakado was striving to clarify his position to the court and clear himself of any suspicion of rebellion.
About half a year later, the situation changed dramatically.
The stage was set in Hitachi Province.
10. Masakado Shelters Fujiwara no Haruaki
In Hitachi Province, tensions between Fujiwara no Haruaki and the provincial officials persisted.
The Shomonki portrays Haruaki as a figure who defied the orders of the provincial officials and caused issues over official goods.
It was Fujiwara no Korehira, the Assistant Governor of Hitachi, who pursued Haruaki.
Hitachi Province was a domain governed by a prince, and in practice, the Assistant Governor managed the provincial affairs locally.
Driven out, Haruaki sought refuge with Masakado.
Masakado accepted Haruaki.
Meanwhile, Prince Koshi, who had clashed with the new provincial officials in Musashi Province, also took refuge with Masakado.
People who opposed the provincial officials began to gather around Masakado.
The conflict with the Hitachi provincial government deepened.
Masakado demanded that the pursuit of Haruaki be halted, but the provincial government refused.
The Shomonki notes that alongside the conflict over Haruaki, the alliance between Fujiwara no Korehira’s son, Fujiwara no Tamenori, and Masakado’s arch-enemy, Taira no Sadamori, was significant in leading to the battle with the Hitachi provincial government.
Autumn of 939.
The confrontation between the Hitachi provincial government and Masakado was becoming inevitable.
11. November 21, 939—The Battle of Hitachi Provincial Government
On November 21, 939 (Tengyo 2).
Masakado led his troops towards the Hitachi provincial government.
This was near present-day Ishioka City in Ibaraki Prefecture.
The Shomonki records Masakado’s forces as numbering over a thousand, while the provincial army had 3,000 men.
Masakado demanded that the pursuit of Haruaki be stopped.
The provincial government refused, and the two armies engaged in battle.
Masakado’s forces emerged victorious.
Fujiwara no Korehira, the Assistant Governor, was captured, and the Shomonki reports that over 300 homes around the provincial government were burned.
Masakado also seized the “seal and key,” symbols of the provincial officials’ authority.
The seal was used by the provincial office for official documents, and the key was for managing the storehouses.
Seizing the seal and key was an act of taking control over the province’s administrative authority.
In 935, Masakado had fought the sons of Minamoto no Mamoru at Nomoto.
In 936, he pursued Yoshikane and others to the Shimotsuke provincial government but did not go as far as to seize control of the government.
Three years later.
Masakado had subdued the Hitachi provincial government, captured the provincial officials, and taken the seal and key.
The conflicts that had been ongoing with his kin and local powers transformed into an armed confrontation with the imperial court’s regional authority with this battle at the Hitachi provincial government.
Masakado’s own position also began to change significantly from this point.
12. To Shimotsuke and Kozuke—and Becoming the “New Emperor”
With Masakado having subdued the Hitachi provincial government, Prince Koshi advised him to expand his actions further.
According to the “Shomonki,” the act of seizing a province was already a grave crime, so it was suggested that he should take control of the entire Kanto region and observe the court’s reaction.
Masakado advanced his troops.
December 11th.
Masakado’s army entered the Shimotsuke Provincial Government Office.
The governor of Shimotsuke, Fujiwara no Hiromasa, and others handed over the official seals, and Masakado took control of them.
By December 15th, he had advanced to the Kozuke Provincial Government Office.
And on December 19th.
At the Kozuke Provincial Government Office, a shamaness, claiming to be a messenger of the Hachiman Great Bodhisattva, proclaimed that Masakado was granted the imperial throne.
The “Shomonki” thereafter refers to Masakado as the “New Emperor.”
Masakado began appointing his brothers and retainers as governors of various provinces in the Kanto region, establishing his own rule.
In February of the 5th year of Shohei (935), four years and ten months after he fought against the sons of Minamoto no Mamoru in Hitachi Province.
Masakado, who had been engaged in armed conflict within his clan, had come to control the provincial government offices of the Kanto region and claimed the title of “New Emperor.”
At that time, news of Masakado’s seizure of the Hitachi Provincial Government Office had reached Kyoto.
The imperial court began to move to suppress Masakado.
Meanwhile, in the Kanto region, Taira no Sadamori, the son of Taira no Kunika, was mobilizing to defeat Masakado.
Joining him was Fujiwara no Hidesato, a powerful samurai from Shimotsuke Province.
In February of the 3rd year of Tengyo (940).
Only two months after claiming the title of “New Emperor.”
Taira no Masakado’s final battle began.
――Continue to the Later Part of the Taira no Masakado Rebellion.
For those who want to delve deeper into the Taira no Masakado Rebellion.
This book offers insights into “Why did Masakado fight?” from both the “Shomonki” and historical perspectives.
Reading the Shomonki (History and Classics) [ Akio Kawashiri ]
