Siege of Koriyama

• Japanese: Battle of Yoshida-Koriyama (吉田郡山城の戦い) (Yoshida Kouriyama no Tatakai)
• Amako Haruhisa (25,000+) vs. Mori Motonari (3,000)\ Sue Harukata (10,000) [after 1540/11]
  • Date: 1540/9-1541/1
  • Location: Aki province
  • Siege

Amako Haruhisa, who had been steadily advancing the power of the Amako (reaching as far west as Harima in 1538), invaded the Môri clan's lands in Aki Province in 1540. Although usually described as the Siege of Koriyama Castle, or the Battle of Yoshida-Koriyama, the affair was in fact a campaign with a number of phases and battles that lasted for the better part of six months.

Môri Motonari had for a time been aligned with the Amako and had been instrumental in the capture of Kagamiyama Castle [鏡山城] in 1523, the same year that Motonari was named as the head of the Mori clan. By the end of the decade Motonari had cut his ties with the Amako and realigned himself with the Ôuchi. Taking advantage of the growing weakness of the Takeda, Motonari grew ever more powerful in Aki Province.

By 1540, the old lord of the Amako, Tsunehisa had nominally retired and turned over the leadership of the clan to his grandson, Haruhisa (also known as Akihisa.) In that year Haruhisa planned a powerful campaign to destroy Motonari and bring Aki under the sway of the Amako. To this end he gathered an army of some 30,000 men from eight provinces (Bitchu, Bizen, Inaba, Iwami, Izumo, Higo, Mimasaka and Aki itself.) The initial phase of the campaign, initiated in the 6th month, involved an attack by the troops of Amako Kunihisa, his brother Hisayuki, and Kunihisa's son Masahisa on the domain of Motonari's ally, the Shishido, a foray that was to prove of little effect except to deny Haruhisa of some of his most capable generals and soldiers for the attack on Koriyama. In the 8th month Haruhisa's main force departed Izumo and advanced into the vicinity of Motonari's Yoshida-Koriyama Castle and established a headquarters at Kazagoshimayama [風越山]. Haruhisa's principal commanders included Kamei Hidetsuna [亀井秀綱], Kikkawa Okitsune [吉川興経], Kokushou Hisazumi, [黒正久澄], Misawa Tameyuki [三沢為幸], Takahashi Mototsuna [高橋元綱], Takao Hisatomo [高尾久友], Yonehara Tsunahiro [米原綱寛] and Yubara Munetsuna [湯原宗綱]. Meanwhile, Motonari evacuated over 5,000 of Yoshida's citizens inside the walls of Koriyama. The castle's walls were defended by around 3,000 soldiers. Urgent requests for aid were dispatched to the Ôuchi in Suo Province.

Two days after arriving, the Amako launched an attack on Koriyama that ended in failure. The Amako then burned Yoshida and various other structures around Koriyama. Motonari responded by sending out a small picked force to engage the enemy and then retreat. The Amako chased the raiders, only to fall into an ambush Motonari had laid out. In the course of the ensuing struggle, Takahashi Mototsuna was slain. In a further action at the end of the month, the so-called Battle of Ikenouchi [池の内の戦い], Môri general Awaya Motoyoshi [粟屋元真] led a sortie out of Koriyama and killed Yubara Munetsuna.

On the 11th day of the 10th month Motonari decided to risk a general engagement with the Amako over the objections of his retainers. Kodama Narimitsu [児玉就光], Kunishi Motosuke [国司元相] and Watanabe Kayou [渡辺通; the reading of his given name may also be Touru] were placed in one ambush with 500 men and Katsura Motozumi [桂元澄] and Awaya Motozane [粟屋元真] were established in another with 200. Motonari himself led the main part of the army and directly engaged the Amako in a hard-fought struggle. The ambush troops then emerged on either side of the Amako and threw them into disorder. The Mori chased the Amako back to their headquarters and caused them significant damage, including the death of Misawa Tameyuki.

The Ôuchi relief army, consisting of 10,000 men led by Sue Harukata, finally departed Suo Province in the 11th month, pausing on Miyajima at offer prayers for victory at the Itskushima Shrine before landing in Aki and marching for Koriyama. They arrived outside Koriyama on the 3rd day of the 12th month, four months after the siege had begun. A series of skirmishes ensued between the opposing armies. Combat intensified in the following month, the 1st of 1541, and largely to the detriment of the Amako. By this time the Amako force that had threatened the Shishido arrived and became heavily engaged in an attack by the Môri and Ôuchi on the Amako's headquarters on Tenjinyama [天神山]. In ensuing action Amako Hisayuki was killed by an arrow and the Amako suffered heavy losses. In the wake of this fight, the Amako retainers, noting the army's dwindling supplies and poor morale, elected to retreat. The Môri and Ôuchi duly pursued but were hindered by snow.

References

• Initial text from Samurai-Archives.com FWSeal & CEWest, 2005
• Rekishi Gunzô Shirizu #49, Môri Senki Gakken, Japan, 1997
• Rekishi Gunzô Shirizu Sengoku no Kassen Taizen Gakken 1997