Assassination of Ōta Dōkan — The Killing of Edo Castle's Founder

The Ōta Dōkan assassination (Ōta Dōkan ansatsu) took place on August 25, 1486 (the 26th day of the 7th month of Bunmei 18), at the Kasuya residence in Sagami Province (Kasuya no yakata, present-day Isehara, Kanagawa Prefecture). Ōta Dōkan, a senior retainer of the Ōgigayatsu Uesugi clan, was murdered on the orders of his lord, Uesugi Sadamasa. Dōkan was a warrior, man of letters, and castle builder of outstanding talent, and he is famous as the builder of Edo Castle. His assassination is a scene that symbolizes the political turmoil of the Kantō in the late Muromachi period, and it also holds notable significance in the history of Japanese swords.

Ōta Dōkan as a Person — A Great Figure Who United Arms and Letters

Ōta Dōkan (1432–1486) was born as the son of Ōta Sukekiyo, a senior retainer of the Ōgigayatsu Uesugi clan. From childhood he studied martial arts and learning, and his cultivation in waka and renga is said to have rivaled that of the leading cultural figures of his day. What made Dōkan's name immortal was the construction of Edo Castle from Kōshō 2 (1456) to Chōroku 1 (1457). On the eastern edge of the Edo plateau in Musashi Province, he built a sturdy hilltop castle (hirayamajiro) and developed it as a military base for the Uesugi clan in the Kantō. Dōkan thus laid, more than a century earlier, the foundation on which the Tokugawa shogunate would later make Edo Castle its seat. Besides Edo Castle, Dōkan was deeply involved in fortification across the Kantō, including building Kawagoe Castle together with his father, Dōshin, and he built his own network of fortresses. Dōkan's military strategy was outstanding. In the wars that frequently broke out in the Kantō during the Bunmei era (1469–1487), he led the forces of the Ōgigayatsu and Yamanouchi Uesugi clans in battles against the Koga kubō, Nagao Kageharu, and others, building a record of unbroken victories. Because Dōkan set up his own military reforms, intelligence gathering, and fortress network, the Uesugi clan's control of the Kantō became stable. As house steward (karei) of the Ōgigayatsu Uesugi clan, Dōkan was responsible for the military and administrative affairs of his main house.

Background to the Assassination — The Lord's Jealousy and the Slander of Retainers

In Bunmei 18 (1486), Uesugi Sadamasa invited Dōkan to the Kasuya residence. When Dōkan came out of the bath, his retainer Soga Hyōgo attacked him on Sadamasa's orders, and he was murdered. There are various theories on the direct reason for the assassination depending on the sources, but the most widely transmitted account is that "Dōkan's power and prestige surpassed those of his lord, and slander came from his close advisers." It is said that a sense of alarm, that Dōkan was so capable that his fame might surpass that of Uesugi Sadamasa, led Sadamasa to resolve on the murder. As a legend connected with the scene of the assassination, it is also transmitted that Dōkan, while wounded, left the words “Tōhō metsubō.” “Tōhō metsubō” was interpreted in later times as a prophetic phrase meaning, "This incident will bring about the collapse of our side (the Uesugi house)." Indeed, after Dōkan's death, the conflict between the Yamanouchi and Ōgigayatsu Uesugi clans intensified, and the politics of the Kantō sank deeper into chaos. The rise of the Later Hōjō clan (Hōjō Sōun) was likewise a result brought about by the self-destruction of the Uesugi clan, which had lost the mediator Dōkan.

Relation to Swords — Blades of the Kantō Warriors in the Late Muromachi Period

The assassination of Ōta Dōkan is also a notable event in the history of swords. Reliable sources on the swords Dōkan favored are few. The Sōshū tradition of the Kamakura and Muromachi periods was a technique developed by master smiths such as Masamune, Sadamune, Hiromitsu, and Akihiro, and its blades are known as masterpieces combining practicality and artistry. In the Bunmei era (late 15th century), when Dōkan was active, the techniques of the Sōshū tradition had already undergone a certain degree of change, but smiths around Kamakura were still active.

Dōkan, who built Edo Castle, came to be spoken of in later history as a figure akin to a "guardian deity of the Kantō."

After the Assassination — The Prelude to the Rise of the Later Hōjō Clan

Seven years after Dōkan's assassination, in Meiō 2 (1493), Hōjō Sōun (Ise Moritoki) invaded Izu Province and opened the way to the rise of the Later Hōjō clan. Edo Castle and Kawagoe Castle, which Dōkan had built, later passed into the hands of the Later Hōjō clan and became bases for their control of the Kantō. With Dōkan's death, the Yamanouchi and Ōgigayatsu Uesugi clans lost a powerful mediator, and the internal strife between the two Uesugi clans, known as the Chōkyō Disturbance (1487–1505), broke out. Taking advantage of this internal strife, Hōjō Sōun wormed his way into southern Kantō, and the path to the Later Hōjō clan's control of the Kantō was opened. The assassination of Ōta Dōkan is historically positioned as the "butterfly's wingbeat" that set off the Sengoku period in the Kantō. His death was not merely the tragedy of a single renowned general; it became the trigger that redrew the political map of the entire Kantō.

Later Evaluation — Revered as a Guardian Deity of Edo

In later times, Ōta Dōkan came to be revered as the founder of Edo (Tokyo). The waka said to have been composed by Dōkan, “Waga io wa / matsubara tsuzuki / umi chikaku / Fuji no takane o / nokiba ni zo miru,” is widely known in later times and conveys the image of Dōkan as a warrior who also had poetic talent. Historic sites and monuments associated with Dōkan remain today in Chiyoda Ward, Tokyo, Isehara City, and elsewhere, and he is remembered as the father of Edo Castle. The meaning of the waka is roughly: "My hut stands where a pine grove stretches on, near the sea; from the eaves I look out at the high peak of Mount Fuji."

Dōkan's Castle-Building Art — Castles Born of the Ideal Joining of Arms and Letters

The castle structure of Edo Castle as developed by Ōta Dōkan made use of the most advanced civil engineering and military technology of the time. Edo Castle was located at the tip of the Musashino Plateau, and it was a strong castle that made the fullest use of its terrain advantage overlooking Edo Bay. Dōkan is said to have set up an archery ground within the castle and had his soldiers practice archery every day. After Dōkan's assassination, Edo Castle continued to function as a base of the Uesugi clan, but its control changed rapidly due to the Chōkyō Disturbance and the rise of the Later Hōjō clan. Ultimately, Tokugawa Ieyasu carried out a large-scale renovation during the Keichō era (1596–1615) and built a huge castle that became the prototype of the present-day Imperial Palace. As a result, the land of Edo that Dōkan chose became the center of Edo (Tokyo), Japan's largest city, and his foresight has been recorded in history for more than 400 years. Dōkan's name continues to shine in Japanese history, today as a symbol of the Kantō warrior spirit and as a great figure who laid the foundation of Edo (Tokyo).