Stories of the Japanese 00240 [Nara] Conquest of the Emishi: The Battle of Subushi

Now, the greatest political challenge that Emperor Konin passed on to Emperor Kanmu was the issue of the Emishi. Although Koreharu no Azamaro had launched a large-scale rebellion in the 11th year of Hoki (780), the government had failed to suppress it, and while no major battles had occurred since then, tax revenue from the Tohoku region remained cut off.
December 7, the 7th year of Enryaku (788). Emperor Kanmu appointed Ki no Kosami as Seito Daishogun (General for the Conquest of the East) and sent him off toward Mutsu. The imperial army gathered at Taga Castle, the seat of the Mutsu provincial government, and on March 9, the 8th year of Enryaku (789), they began their advance, splitting into several routes.
On March 28, an imperial force of 20,000 to 30,000 soldiers crossed the Koromo River (Hiraizumi Town, Iwate Prefecture) and set up camp on the north bank. This army was commanded by the deputy envoy, Iruma no Hironari.
However, after this, Iruma no Hironari remained stationed there and made no attempt to move at all. Losing patience, Emperor Kanmu urged him to launch an attack on May 12.
Upon hearing the Emperor's reprimand, Iruma no Hironari hurriedly ordered an advance. As they crossed the Kitakami River and marched north along the east bank, they encountered about 300 Emishi soldiers in a chance engagement.
It was a battle between an imperial army of over 2,000 and an Emishi force of only about 300. Seeing that they were outmatched, the Emishi force retreated to the north, and the imperial army pursued them. During the pursuit, they reached a place called Subushi Village (Oshu City, Iwate Prefecture).
At this time, the temporary retreat of the Emishi force was likely a feint.
Suddenly, 800 Emishi soldiers appeared before the imperial army, which had been pursuing the enemy with momentum, and a battle ensued. With the fierce intensity of the Emishi forces, the imperial army was pushed back. Then, 400 Emishi soldiers who had been hiding on the mountain launched a new surprise attack. The imperial army was cornered in a narrow space between the mountain and the river, collapsed completely, and fell into the river one after another.
In this Battle of Subushi, the imperial army suffered 1,061 deaths. The breakdown is said to be 25 deaths in combat and 1,036 deaths by drowning. On the other hand, since 1,502 soldiers survived, it means that a full 40 percent were killed in action. It was truly a staggering and disastrous defeat.
In June, Ki no Kosami, having heard the news of the disastrous defeat at Taga Castle, decided to abandon the conquest of the Emishi and sent a memorial to the capital stating, 'I wish to disband the army and return to the capital.' Upon receiving this memorial, Emperor Kanmu was enraged and reprimanded them, stating that 'the commanders are incompetent.'
The Emishi commanders who dealt such a devastating blow to the numerically superior imperial army were the chieftains Aterui and More. Aterui and More were truly brilliant tacticians, and I believe it was likely this Battle of Subushi that etched their names into the memory of Emperor Kanmu.
After this, the conquest of the Emishi was not carried out for about six years. It would not be until the Heian period that the conflict between the imperial army and the Emishi forces would be resolved.