INTERACTIVE BATTLE
Siege of Yoshida-Koriyama
September 1540 · Yoshida-Kōriyama Castle
Amago Haruhisa attacked Yoshida-Koriyama Castle, but Mōri Motonari defended it with Ōuchi reinforcements.
Background
Mōri Motonari switched to the Ōuchi faction in 1525 and by 1529 had destroyed the Takahashi clan, who supported the Amago, alongside the regional lords (kunin) of Aki and Iwami provinces, inheriting their dominant position. Against the expanding Mōri, in 1540 (Tenbun 9), Amago Haruhisa of Izumo Province led a large army into Aki and established his main camp at Kazakoshiyama, about 4 km from Goryōzan Castle.
Outcome
The Amago army moved their main camp to Aoyama and Mitsui castles overlooking Goryōzan and spent four months building a siege ring, but Motonari held the castle while cutting off the Amago army's supply lines. On January 13, 1541 (Tenbun 10), Sue Harukata, leading Ōuchi Yoshitaka's reinforcements, attacked Mitsui and killed Amago Haruhisa's uncle Hisayuki in fierce combat, after which the Amago army collapsed and retreated to Izumo.
Course of the battle
1 September 1540
Amago Haruhisa Establishes Main Camp at Kazakoshiyama
Amago Haruhisa's large army, which invaded Aki, constructed Kazakoshiyama—located approximately 4 km in a straight line from Kōriyama Castle and the highest point in the mountainous area around Yoshida—as a siege castle serving as his initial main camp.
Sources345·Certainty: Medium
2 1540
Amago Forces Build Siege Castles at Aoyama and Mitsuiyama, Besieging Kōriyama Castle
The Amago forces constructed a massive integrated siege castle system comprising Aoyama Castle and Mitsuiyama Castle—adjacent fortifications separated by a valley—opposite Kōriyama Castle, taking four months to complete.
Sources235·Certainty: Medium
3 January 13, 1541
Decisive Battle at Mitsuiyama; Amago Forces Withdraw
The Ōuchi relief forces, commanded by Sueharada Takashiro, attacked Mitsuiyama. In a fierce engagement, Amago Hisayuki, the great-uncle of Amago Haruhisa, was killed in action. The Amago forces subsequently collapsed and retreated.
Sources235·Certainty: High
Historical significance
Motonari's victory at Goryōzan Castle cemented the Mōri position as the center of Aki's regional lords. In May of the same year, the Aki Takeda clan, who had been supported by the Amago, was destroyed, and the Mōri expanded their influence toward the Hiroshima Bay area.
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Key figures
毛利氏
1
Castle Lord of Koriyama
Defended Koriyama Castle against the Amago assault from September 1540 for about half a year.
Sources3·Certainty: High
尼子氏
1
Commander-in-chief of the Amago forces (Haruhisa during the Aki invasion)
After establishing his headquarters at Kazeokoshi Castle, he relocated to Aoyama and Kōi castles to besiege Koriyama, but was defeated by Ōuchi reinforcements and withdrew to Izumo in January 1541.
Sources23·Certainty: High
大内氏
1
Ōuchi reinforcement commander (then named Sue Takafusa)
Under orders from Ōuchi Yoshitaka, he led reinforcements into Aki and attacked and defeated the Amago positions at Kōi (Mitsuka) on January 13, 1541.
Sources2·Certainty: High
Notes on the data
The Amago army's arrival date (September 4), troop numbers (around 30,000), the date of the Ōuchi reinforcements' arrival (December 3), and their camp locations (Yamada Nakayama and Sumiyoshi Mountain) appear in civilian sources but are not documented in official records confirmed by this research and are not included in the text.
Sources consulted
- 安芸高田市「郡山城跡（吉田町）」
- 安芸高田市「青光井山尼子陣所跡（吉田町）」
- 安芸高田市『安芸高田市史跡ガイドブック』
- 安芸高田市歴史民俗博物館「毛利氏関係史跡」
- 国土地理院 地名検索・標高API
The numbers in the text refer to the list above. Certainty indicates how far a statement is supported by the cited sources; it does not refer to the precision of the coordinates or the dating.
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