Battle of Gōrozaka
Date: Ninth month of Eiroku 2 (1559)
Location: Gōrozaka near Yamabuki Castle in Iwami Province
Outcome: After a long expedition, and owing to other conflicts in northern Kyūshū, the Mōri abandoned their assault against the stronghold of Yamabuki Castle and during the retreat were overtaken by Amago forces.
The Battle of Gōrozaka occured in 1559 at Gōrozaka near the stronghold of Yamabuki Castle in Iwami Province. In this battle, the Mōri clan (the sengoku daimyō of Aki Province) suffered a major defeat in fighting against the Amago clan (the sengoku daimyō of Izumo Province).
In 1556, Mōri Motonari invaded Suō and Nagato provinces in an event known as the Invasion of Bōchō. At the same time, his second son, Kikkawa Motoharu, advanced into Iwami, and by subjugating Sasuka Naganobu, seized control of Iwami Silver Mine, an important center for mining operations. Either in 1556 or 1558, Amago Haruhisa, a sengoku daimyō and the head of the Amago clan based in Izumo Province, achieved a resounding victory over Shishido Takaie, a retainer of the Mōri, in a battle known as the Collapse at Oshibara (Oshibara kuzure). This enabled the Amago to dispossess the Mōri of Yamabuki Castle and the Iwami Silver Mine. The Amago clan placed Honjō Tsunemitsu in Yamabuki to protect the mine. In addition, Ogasawara Nagakatsu, the head of the powerful Ogasawara clan in Iwami, joined with the Amago to oppose the Mōri, becoming a major impediment to invading Iwami.
Details of the battle
In 1558, Mōri Motonari made another attempt to seize Iwami Silver Mountain by bringing Kikkawa Motoharu and Kobayakawa Takakage to lead an attack on the base of the Ogasawara clan at Nukuyu Castle. Nagakatsu requested help through Tako Tokitaka, a retainer of the Amago, whereupon the Amago responded by sending reinforcements but, either that year or the next, surrendered in the eighth month of 1559.
Attack against Yamabuki Castle
After this victory, Motonari began to attack assorted castles aligned with the Amago in the environs of the Iwami Silver Mine. In the ninth month of 1559, an army sent to attack the Iwami Silver Mine with Ogasawara Nagakatsu in the vanguard (under the command of the Mōri) set-up a base on Sennoyama in front of Yamabuki Castle. The Mōri army totaled as many as 14,000 soldiers, but Honjō Tsunemitsu and his men vigorously defended the castle.
Pursuit by the Amago army
Perhaps owing to the arduous expedition to the reach the destination, Motonari realized that it would not be easy to topple Yamabuki. Moreover, around this time, Ōtomo Yoshishige, a sengoku daimyō and head of the powerful Ōtomo clan of Bungo Province, began to attack the base of the Mōri in Buzen Province at Moji Castle, an event known as the Third Battle of Moji Castle. This led Motonari to cease the attack on Yamabuki and withdraw his forces.
While coming down Gōrozaka, the Mōri army began to retreat toward Yunotsu, but during this retreat, were pursued by the Amago forces. The defenders of Yamabuki Castle, led by Tsunemitsu, along with the defenders of other castles that had not until then showed movement, converged to launch the counterattack, catching the unsuspecting Mōri forces by surprise and forcing them to flee in defeat. The main division under Amago Haruhisa also is noted to have joined in the attack.
In the midst of the ensuing chaos, Motonari himself barely escaped with his life. Gōrozaka had formerly served as the path of retreat for the Mōri when the expedition to Izumo by Ōuchi Yoshitaka failed (an event known as the First Battle of Gassantoda Castle). Seven mounted soldiers including a retainer named Watanabe Tōru sacrificed themselves for Motonari. Under another theory, this episode occurred during the Battle of Gōrozaka.
Consequences of the battle
The artful tactics of Tsunemitsu succeeded in compelling the Mōri army to retreat. Afterwards, Haruhisa returned from Ōta to Izumo Province, while the Amago achieved a strategic victory in defending the Iwami Silver Mine.
After the loss, Motonari faced enemies in the form of the Ōtomo clan of northern Kyūshū and the Amago clan of the Sanin region. In addition, Fukuya Takakane, a kokujin from Iwami affiliated with the Mōri, rebelled and joined forces with the Amago. Motonari was unable to re-capture Iwami Silver Mine during Haruhisa’s lifetime. Motonari did not regain control of the site until, following the sudden demise of Haruhisa, he entered into the Unkei Accord (a settlement between the Amago of Izumo and the Mōri of Aki), toppled the base of Fukuya Takakane at Honmyō Castle in the Naka District of Iwami, and ensnared Honjō Tsunemitsu in 1562.