Nagoya Castle’s Aomatsuba Incident

The Aomatsuba Incident was a mysterious incident that occurred at Nagoya Castle on February 16, 1868. Between February 16^th and the 21st, 1868, 14 high-ranking retainers of the Owari Tokugawa clan were suddenly captured and executed within the grounds of Nagoya Castle, and another 20 were imprisoned and demoted. Three were chief retainers of the Owari Tokugawa clan.

4 high-ranking retainers of the Owari Tokugawa clan were suddenly captured and executed within the grounds of Nagoya Castle

Watanabe Shinzaemon

The 14 samurai were rounded up, arrested and beheaded in an area of Nagoya Castle’s Ni-no-Maru, where the Aichi Prefectural Gymnasium, site of the annual Summer Sumo tournament, currently takes place.

Records remain as to who was arrested and executed and when.
Those who were beheaded were:

Feb. 16:
Watanabe Shinzaemon aged 49 (with an income of 2,500 koku. A koku was about 180 liters of rice, or the amount required to feed a man for a year, and the value by which samurai were paid)
Sakakibara Kageyu, 59 (1,500 koku)
Ishikawa Uzojo, 42 (1,000 koku)

Feb. 17
Uda Yutaro, 61
Yasui Chojuro, 52
Terao Takeshiro, 54 (150 koku)
Baba Ichiemon, 26 (200 koku)

Feb 19.
Takeno Shinzaemon, 77 (800 koku)
Naruse Kasei, 62 (800 koku)

Feb. 21
Yokoi Sakon (?) 51, (4,000 koku)
Hayashi Nobumasa Monzaburo, 40 (300 koku)
Matsubara Shinshichi, 41
Yokoi Magoemon, 44 (1500 koku)
Sawai Kozaemon 44 (800 koku)

((?) readings of some of the given names may be incorrect)

Why they were arrested, and why they were suddenly killed has remained one of the dark secrets of Nagoya Castle. There are many theories.

Why they were arrested, and why they were suddenly killed has remained one of the dark secrets of Nagoya Castle

Tokugawa Yoshinobu

The Owari Tokugawa clan were one of the three main braches of the ruling Tokugawa House, along with Mito and Kii. Economically, and influentially the strongest was Owari, and naturally the Owari clan had long been staunch supporters of the shogun. However, 1868 was a time of great political turmoil in Japan. The country was afraid of foreign invasion following the visit by an American warship under Commodore Perry in 1854, which further weakened the power and prestige of the Shogunate. The nation was on the brink of bankruptcy as the financial reforms instigated by the Tokugawa had failed. The 15^th shogun, Tokugawa Yoshinobu had already written out and presented his resignation to the Imperial house, and remained in isolation.

The Shogun’s remaining forces had been defeated in the Battle of Toba-Fushimi between January 3-5, 1868. Although many samurai now agreed to restore power to the Emperor, there were still large numbers of samurai remaining loyal to the Tokugawa. Shogun Yoshinobu was even considering having his resignation annulled.

Naturally, there were such factions within Nagoya Castle too. Nagoya Castle was located between Kyoto and Edo, it was an influential region, and financially stable. It was therefore seen as a potential hotbed of dispute. If samurai within Nagoya Castle fought to re-instate the Shogun, then others may follow, and the nation would erupt into a destructive and bloody civil war. The national authorities realized this, and suggested to the lord of Nagoya Castle, Tokugawa Yoshikatsu, that something be done in advance to quell any potential uprising.

Tokugawa Yoshikatsu, Lord of Nagoya Castle

For that reason, pro-shogunate activists within Nagoya Castle’s hierarchy were quickly identified, rounded up, and quickly and quietly executed. Neither they, nor their families were told of the reasons. It appears that this was seen by the Shogunate as Yoshikatsu having taken a step too far, and in embarrassment, the incident was hushed up, and explained as a trivial, in-clan matter.

Three years later, pardons were granted to those killed and imprisoned, and their names were reinstated in the Nagoya Castle samurai registry.

The Aomatsuba Incident is so named as Watanabe Shinzaemon, one of the first to be executed, lived in a residence known as Aomatsuba, just outside of Nagoya Castle’s soto-bori, outer moat. (incidentally, the site of his residence is about 300m from my house!)

Modern day site of the Aomatsuba residence

A small memorial stone was erected in 1926 near the actual execution site, but later mysteriously disappeared. A current memorial stone can be found behind the toilet block at the eastern entrance gate to Nagoya Castle, and a small sign has been erected in the Ni-no-Maru area. The actual site of the executions is believed to have taken place about 100m south of the current stone site.