Battle of Imayama
Date: Fourth month to 8/20 of Genki 1 (1570)
Location: Mount Ima near Saga Castle in Hizen Province in northwest Kyūshū
Outcome: Aiming to expand his territory, Ōtomo Sōrin sent forces into Hizen to subjugate Ryūzōji Takanobu, but after a long siege of Saga Castle by the Ōtomo, the Ryūzōji launched a successful nighttime attack, defeating the Ōtomo and sending them fleeing back to Bungo Province.
The Battle of Imayama occurred from the fourth month to 8/20 of Genki 1 (1570). This conflict was waged between Ōtomo Sōrin (a sengoku daimyō from Bungo Province) and Ryūzōji Takanobu (a sengoku daimyō from Hizen Province) in northern Kyūshū.
Prelude to the conflict
From their base in Bungo Province, the Ōtomo extended their influence into Buzen and Chikuzen provinces. In Hizen Province, the Ryūzōji clan (who served the Shōni clan) were expanding their authority. After the fall of the Shōni, Ryūzōji Takanobu, the head of the clan, allied with the Ōuchi of Suō Province to steadily expand his territory. Following the demise of Ōuchi Yoshitaka, Takanobu established friendly relations with the Mōri and had an antagonistic relationship with the Ōtomo.
Seeking to advance into Kyūshū, around 1561, the Mōri clan launched a full-scale invasion of Kyūshū. In the fifth month of 1569, the Mōri toppled Tachibanayama Castle in Chikuzen, and used it as a bridgehead from which to challenge the Ōtomo. However, taking advantage of the absence of the main force of the Mōri army, former retainers of the Amago clan that had been destroyed by the Mōri raised arms in Izumo Province, causing Motonari to withdraw his forces from Kyūshū.
Details of the battle
Upon learning of these developments, Takanobu assembled a garrison at Saga Castle and prepared to hole-up and resist the daunting forces from the Ōtomo. In addition to his own family, he called upon senior retainers including the Nabeshima, the Ogawa, and the Nōtomi to assemble a force of about 5,000 men. To confront the Ōtomo, Takanobu positioned his forces as follows:
- East entrance: Nabeshima Nobufusa and Nabeshima Nobushige (brothers) and Ogawa Nobutoshi
- South: Ryūzōji Naganobu (younger brother) to defend against naval forces
- West: Ryūzōji Akikane and Ryūzōji Nobuchika (younger brother)
- North: Ryūzōji Ienari and Nōtomi Nobukage
The conflict unfolded with a series of small-scale clashes over a period of months. Despite laying siege to Saga Castle with a large army, the Ōtomo forces could not make much progress against stiff resistance from the Ryūzōji garrison who maintained high spirits.
On 4/23, the Ryūzōji forces unexpectedly burst out in a bid to slash their way through the camp of Tachibana Dōsetsu. In the fifth month, the armies shot arquebuses across a river divide, and, in the seventh and eighth months, battles against the Ōtomo navy occurred in the Bubai Harbor and on the Chikugo River. None of these clashes, however, proved decisive or gave the Ōtomo an opportunity to advance. Nevertheless, the Ryūzōji did not anticipate the arrival of reinforcements needed for a prolonged war, and if the status quo remained the same, would eventually face capitulation.
Meanwhile, Sōrin grew impatient with the inability of the large army to overtake Saga Castle. Sōrin then sent 3,000 soldiers commanded by his younger brother (or nephew), Ōtomo Chikasada, to the front lines, ordering Chikasada to launch a full-scale assault against the castle.
On 8/17, Chikasada marched through the Kanzaki District to set-up a camp on Mount Ima located to the north of Saga Castle on the border of the Ogi District. He decided to lead a full-scale assault against Saga Castle on 8/20. However, on the night before the planned assault, Chikasada planned a saké event as a pre-celebratory ritual at the camp on Mount Ima. After news of these plans was intercepted by the Ryūzōji, Nabeshima Nobuo recommended a nighttime attack against Chikasada’s forces on Mount Ima.
On the evening of 8/19, a deliberation ensued among the Ryūjōji forces in Saga Castle with some arguing to continue resisting while others called for surrender. At first, the proposal for the attack was dismissed as reckless, but the plan gained support from among others, Narimatsu Nobukatsu, and, after Takanobu’s natural mother, Keigin-ni, shouted a war cry. A small battalion led by Nobuo was formed for the surprise attack.
Beginning from the evening of 8/19 until the break of dawn on 8/20, the forces under Nobuo departed the castle and slipped through the surrounding enemy forces to set-up behind the main base of the Ōtomo on Mount Ima. This battalion was joined by a unit led by Hyakutake Tomokane as well as local bushi and villagers, and a detached unit led by Nōtomi Nobukage (a retainer of the Ryūzōji) swelling the force of several hundreds of fighters.
The night before the attack, Chikasada’s army had been in high spirits with a feeling that victory was at hand. At early dawn, upon the signal from Nobuo, the forces launched their surprise attack against Chikasada’s camp. As the attacking soldiers surged into the camp, the Ōtomo forces quickly descended into chaos, including death by friendly fire. A group of six soldiers thrust at Chikasada to lie him down while Narimatsu Nobukatsu killed him. Having lost their commander-in-chief, the Ōtomo troops scattered in retreat. With the attacking forces in pursuit, the situation reversed in a moment of time, and while the surprise attack yielded success for the Ryūzōji, the Ōtomo lost over 2,000 soldiers.
Aftermath of the battle
Riding on the momentum of this victory, on the following day of 8/21, the Ryūzōji forces captured Kajimine Castle, and, on 8/23, prevailed in a battle at the entrance to Takao (Takamine) under Saga Castle.
To commemorate the victory, Nobuo changed the crest for the Nabeshima family from 剣 flower-shaped crest to the apricot flower crest of the Ōtomo.
Owing to the limited scale of the Battle of Imayama, it did not significantly undermine the large army of the Ōtomo. Nevertheless, after a siege of Saga Castle lasting one-half year, the Ōtomo were unable to prevail. At the end of the ninth month of 1570, the Ryūzōji proposed a settlement (through Tajiri Akitane of Chikugo Province) by offering to tender Takanobu’s younger brother, Ryūzōji Nobuchika, as a hostage, to which the Ōtomo agreed. The settlement was reached on 10/1 while Ōtomo Sōrin withdrew with his army to his home province of Bungo.
Although Ryūzōji Takanobu achieved victory at the Battle of Imayama, it was a limited-scale conflict so it did not eliminate governance by the Ōtomo of Hizen. As a result, he continued to demonstrate subordination to the Ōtomo. Upon the invasion by the Ōtomo, Takanobu subdued many rebellious gōzoku, or powerful local families in the area, emerging along with Ōtomo Sōrin and Shimazu Yoshihisa as one of the three most powerful sengoku daimyō in Kyūshū.