Mori Motonari (1497–1571), head of the powerful Mori clan, was one of the most influential daimyo in the Chugoku region, located in western Honshu. During the turbulent and violent Sengoku Jidai period, he waged continuous wars in an effort to expand his domain and strengthen his clan's power.
As early as 1543, Motonari had already attempted to seize Gassan-Toda Castle from his neighbor, Amago Haruhisa, but that attempt ended in failure. However, in 1561, Haruhisa died, and two years later, Motonari launched a new military campaign with the aim of conquering Izumo Province.
In order to isolate the enemy's main fortress, Motonari began to systematically capture the remote fortifications belonging to the Amago clan. Among them, the most significant was Shiraka Castle, the largest of the satellite castles (shijo), which was of key importance for defending the approaches to Gassan-Toda. In the fall of 1563, Motonari began his siege. The new head of the Amago clan, Yoshihisa, sent troops to help the besieged, but they were intercepted by Mori's army and defeated. The siege of Shirakawa lasted 70 days and ended in surrender after the besiegers managed to cut off the castle's water supply. The commander of the garrison, Matsuda Michihisa, chose to commit suicide rather than surrender to the enemy.
In the spring of 1564, Motonari approached the walls of Gassan-Toda. This citadel, which belonged to the Amago clan, was one of the five largest mountain castles of its time. Although Gassan-Toda was a yamajiro (mountain castle), it had a highly developed system of defensive structures. In addition to the traditional three courtyards—defensive lines located at the top of Mount Gassan—the fortress had other courtyards that descended in terraces down to the Toda River (now known as Iinashi) and its tributary.
The first attempt to storm the castle, protected by natural conditions and powerful fortifications, was unsuccessful. Mori's army suffered losses, and Motonari was forced to retreat to regroup his forces. In the summer of the same year, he returned to Gassan-Toda with an army of 25,000 samurai. At that time, the castle garrison numbered about 10,000 soldiers. This time, Motonari abandoned the idea of a direct assault and decided to wear down the fortress.
A long blockade began. Motonari issued an order not to accept defectors, thereby contributing to the rapid depletion of food supplies among the besieged. At the same time, he carried out a cunning political maneuver, using the well-known strategy of “killing with someone else's knife.” The head of the Amago clan, Yoshihisa, had a loyal vassal, Uyamahisakane, who was known as a skilled strategist and wise advisor. Motonaori, with the help of his agents, spread rumors among Yoshihisa's people that Hisakane was allegedly preparing to betray him. The false accusations achieved their goal — Yoshihisa believed them and ordered the execution of his valuable assistant. This act seriously undermined the morale of the castle's defenders.
Ultimately, when Motonari lifted the ban on accepting defectors, thousands of exhausted and half-starved Amago warriors abandoned their positions and fled the fortress. By the beginning of winter 1565, the situation inside the castle had become hopeless, and Yoshihisa decided to surrender. To the surprise of many of his contemporaries, Motonari showed mercy and spared the life of his defeated enemy. Yoshihisa was allowed to become a monk and go into exile at Enmyoji Temple in Aki Province.
See also
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The Siege of Inabayama Castle
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The Siege of Wado Castle
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The siege of the Ishimama Honganji monastery
In Japanese history, the siege of Ishiyama Hongan-ji — the main stronghold of the Ikkō-ikki movement during Oda Nobunaga’s campaign — is considered the longest, lasting from August 1570 to August 1580.
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The Battle of Norada
The Battle of Norada is a striking example of a clash during the Sengoku Jidai period, when numerical superiority did not always guarantee victory, even in open battle.
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Battles of Kawanakajima
The Battles of Kawanakajima were a series of fierce conflicts during Japan's Sengoku period, waged between Takeda Shingen of Kai Province and Uesugi Kenshin of Echigo Province from 1553 to 1564. These battles centered around the strategic Kawanakajima plain, lying between the Sai and Chikuma rivers in northern Shinano Province, now within Nagano City. The rivalry began when Shingen took control of Shinano, forcing Ogasawara Nagatoki and Murakami Yoshikiyo to seek refuge with Kenshin, prompting repeated clashes.
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Siege of Odawara 1590
The Third Siege of Odawara in 1590 was a pivotal moment in Toyotomi Hideyoshi's efforts to neutralize the Hojo clan as a challenge to his authority. In the months leading up to the siege, the Hojo made significant, hurried improvements to the castle's defenses as Hideyoshi’s intentions became clear. However, despite Hideyoshi's overwhelming force, there was little actual combat during the siege.
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Battle of Tenmokuzan
The Battle of Tenmokuzan in 1582 is remembered as the final stand of the Takeda clan in Japan. This battle marked the last attempt by Takeda Katsuyori to resist Oda Nobunaga's relentless campaign against him. Fleeing from his pursuers, Katsuyori set fire to his fortress at Shinpu Castle and sought refuge in the mountains at Iwadono, a stronghold held by his loyal retainer, Oyamada Nobushige. However, Oyamada betrayed Katsuyori, denying him entry. Left with no other option, Katsuyori committed suicide alongside his wife, while the remnants of his army made a valiant effort to hold off their attackers.
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Battle of Oshu
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