Sakuradamon Incident

Sakuradamon Incident——The Greatest Political Assassination of the Late Tokugawa Period

On the morning of March 3, 1860 (Manen 1), outside Sakuradamon Gate of Edo Castle (present-day Chiyoda Ward, Tokyo). In the quiet, snow-covered dawn, one of the most famous political assassinations in Japanese history was executed. A procession of Tairō (senior councilor) Ii Naosuke, the highest authority in the shogunate, was ambushed by 18 samurai assassins defected from Mito and Satsuma domains, and Naosuke was assassinated. This 'Sakuradamon Incident' was the moment when the authority of the Edo Bakufu was irreparably damaged, and it marked the beginning of the countdown to the Meiji Restoration——a historic turning point.

Background to the Sakuradamon Incident——The Ansei Purge and Its Backlash

In 1858 (Ansei 5), Ii Naosuke, as Tairō of the shogunate, signed the Japan-US Treaty of Amity and Commerce. Because this treaty was concluded without imperial sanction from the emperor, it was fiercely criticized as an 'unauthorized treaty' by the imperial court and the Sonnō Jōi faction (those advocating reverence for the emperor and expulsion of foreign powers).

Naosuke attempted to suppress this criticism by force, instituting the 'Ansei Purge (1858–1859).' Over 100 daimyo (feudal lords), court nobles, and samurai activists of Sonnō Jōi and anti-shogunate sympathies were punished, and notable figures such as Yoshida Shōin and Hashimoto Sanai were executed.

The backlash from Mito Domain (one of the Tokugawa Three Houses) against this authoritarian rule was particularly intense. Mito Domain had a strong tradition of 'reverence for the emperor' and viewed Naosuke's actions as those of a 'traitor who disrespected the imperial court.' Some Mito domain samurai defected from their domain and planned Naosuke's assassination.

The 18 Assassins——Snowy Sakuradamon Gate

The assassination plot was planned by a group of rōnin, chiefly former samurai of Mito who had defected from their domain. The principal planner was Seki Tetsunosuke, and Arimura Jizaemon, a samurai defected from Satsuma Domain, also participated. The plot was prepared over several months, and March 3 (Hinamatsuri, the Dolls' Festival) was chosen as the execution date——on this day, festivities were held in Edo Castle, and it was expected that the Tairō's escort would be in formal ceremonial dress (formal kimono rather than armor).

On that day, Edo was snow-covered. The escort of approximately 60 samurai from Hikone Domain, protecting themselves against the cold, was marching with cloth bags covering the hilts of their katanas (in the state of 'sheathed swords'). This proved disastrous——when the moment came, the swords could not be drawn quickly.

The rōnin ambushed the procession outside Sakuradamon Gate. Arimura Jizaemon first rushed at Naosuke's palanquin and slashed at Naosuke inside. The Hikone domain samurai guards, struggling with their bagged swords, counterattacked, but in the chaos Naosuke was killed. Naosuke's head was taken by Arimura Jizaemon (Arimura himself sustained grave wounds and later took his own life).

Among the assassins, many were killed on the spot or took their own lives from severe wounds; those who survived were later executed.

The Sakuradamon Incident and Japanese Katanas——The Legend of the 'Thin Blade of Sakuradamon'

The Sakuradamon Incident is also a fascinating event from the perspective of practical combat use of Japanese katanas. Many of the swords actually used by late-Tokugawa samurai activists reflected the sword culture of that era.

Among the major swordsmiths of the late Tokugawa period were Koyama Muneji, Gen Kiyomaro (Kiyomaro), and Nagasone Kotetsu. The swords forged by these smiths, designed as robust blades for actual combat in the late Edo through late Tokugawa periods, were treasured by the samurai activists.

Furthermore, Mito Domain possessed its own distinctive sword culture, and swords known as 'Mito Masamune' and 'famous swords of the Mito Tokugawa house' were passed down through the domain. Many of the swords used by Mito domain samurai embodied the spirit of reverence for the emperor.

Swords made by Koyama Muneji were particularly highly regarded among late-Tokugawa swordsmen and their schools. Koyama Muneji was a representative swordsmith of the late Edo period, and his works combined practical combat effectiveness with artistic merit.

Regarding the swords used in the Sakuradamon Incident, there are accounts that the 'thin blades' used by the assassins broke one after another while parrying the guards' swords, illustrating the ferocity of the melee that day. The special circumstances of a sword fight in falling snow was a scene where blade quality directly determined survival.

What the 'Snowy Sakuradamon' Tells Us——The Symbolic Collapse of Shogunal Authority

The Sakuradamon Incident transcended a mere assassination in its significance because of its symbolic weight: 'the highest authority of the shogunate was killed in the public streets.'

Throughout the Edo period, the authority of the shogunate rested upon 'the guarantee of public peace' and 'the maintenance of samurai order.' The fact that in the very heart of Edo, at the seat of shogunal power, the Tairō——the supreme authority holder——was killed by 18 rōnin demonstrated to the realm that the shogunate had 'lost its ability to maintain public peace.'

After this incident, late-Tokugawa political assassinations multiplied. The Ikedaya Incident (1864), the assassination of Sakamoto Ryōma (1867), and ultimately the Boshin War——the Sakuradamon Incident was the origin point of this cascade.

The late-Tokugawa political conflicts over 'expel the barbarians or open the country' and 'overthrow the shogunate or support it' moved toward resolution through the actions of sword-wielding samurai activists. The snow that fell at Sakuradamon Gate may have been an omen that the Edo Bakufu, which had boasted 260 years of peace, would crumble away like melting snow.