Siege of Koriyama

What Happened

The siege of Yoshida-Kōriyama Castle (吉田郡山城の戦い, Yoshida-Kōriyama-jō no tatakai) ran from the 6th day of the 9th month of Tenbun 9 — 5 October 1540 — to the 13th day of the 1st month of Tenbun 10, 8 February 1541. It was fought at Yoshida-Kōriyama Castle in Yoshida, Aki Province, in the west of the main island of Honshu.

The attacker was Amago Haruhisa, who brought an army of 30,000 men against the castle. The castle belonged to Mōri Motonari and was held by a garrison of 8,000. The defenders were outnumbered by nearly four to one and spent the winter under blockade.

The siege was broken from outside. The Ōuchi clan, a great power in the region, sent an army to relieve the castle under the command of Sue Harukata. Faced with a relieving force on top of a garrison that had not surrendered, the Amago abandoned the siege and withdrew.

Background

The siege belongs to the Sengoku period (戦国時代, sengoku jidai), the century and a half of near-continuous regional warfare that ran from the middle of the fifteenth century into the early seventeenth. It also falls within the Muromachi period (1336–1573), the era named for the Muromachi district of Kyoto where the Ashikaga shoguns had their seat. By 1540 the shogun's authority counted for little in the provinces, and power lay with daimyo — regional lords who raised their own armies and fought their own wars.

The Amago were one such house, based in the mountains of Izumo Province on the Japan Sea side. Amago Haruhisa was pushing south-east into Aki Province, the coastal territory that faces the Inland Sea. The Mōri were a smaller clan rooted in Aki, and Yoshida-Kōriyama Castle was their stronghold. The Ōuchi, who dominated the western end of Honshu from their base in Yamaguchi, were the Mōri's powerful neighbours and the natural counterweight to Amago expansion.

The campaign is dated by the Japanese era system (年号, nengō), in which years are counted afresh from the start of each era. Tenbun (天文, tenbun) was the era name in use, so the siege began in the 9th year of Tenbun and ended in the 1st month of the 10th.

Why It Mattered

The failure at Yoshida-Kōriyama checked Amago Haruhisa's advance into Aki at the moment it seemed most likely to succeed. An army of 30,000 that could not take a castle held by 8,000, and that then withdrew rather than fight the Ōuchi relief force, had spent its strength without gaining the ground it came for.

For the Mōri, survival was the whole point. Mōri Motonari held his castle through a winter siege and kept his clan intact in a province contested by far larger neighbours. The defence of Yoshida-Kōriyama became the first in the sequence of contests by which the Mōri would later overturn the Amago and take their place among the great houses of western Japan.

The siege also shows the mechanics of Sengoku warfare in miniature: a castle as the anchor of a clan's territory, a numerically superior attacker forced to sit down before it, and a third party — here the Ōuchi under Sue Harukata — whose decision to march determined the outcome without the castle itself ever falling.

The Name in Japanese

The Japanese name is 吉田郡山城の戦い, read よしだこおりやまじょうのたたかい (Yoshida-Kōriyama-jō no tatakai).

It breaks down as follows:

• 吉 — read yoshi here. It means "good fortune" or "auspicious".
• 田 — read da here (from ta, "field"). It means "rice field" or "paddy".
• 郡 — read kōri here. It means "district" or "county", an old administrative unit.
• 山 — read yama. It means "mountain".
• 城 — read jō here (from shiro). It means "castle".
• の — read no. A possessive particle linking the castle name to the word for battle.
• 戦 — read tatakai. It means "battle" or "war".
• い — read i. The kana ending of tatakai.

So 吉田郡山城 is the castle's name: Yoshida, the place; kōriyama, "district mountain"; and jō, "castle". The final の戦い turns the whole into "the battle of Yoshida-Kōriyama Castle". Note that the castle's name is often written in romaji as Kōriyama, with the macron marking the long ō; the same sound appears in the kana こおり.

Key Figures

Amago Haruhisa commanded the attacking army of 30,000. He led the Amago house from Izumo Province and pressed into Aki Province in 1540, investing Yoshida-Kōriyama Castle in the 9th month of Tenbun 9.

Mōri Motonari held Yoshida-Kōriyama Castle with a garrison of 8,000. His defence of the castle through the winter of 1540–41 ended with the Amago withdrawal.

Sue Harukata commanded the Ōuchi army sent to relieve the siege. His march on the castle forced the Amago to abandon the investment.

Amago Kunihisa is associated with the conflict on the Amago side.

Yoshida-Kōriyama Castle itself, in Yoshida in Aki Province, was the object of the siege and the Mōri stronghold.