Siege of Sanbonmatsu Castle


Ōuchi Clan

Iwami Province


Yoshimi Clan

Date:  Third to eighth months of Tenbun 23 (1554)

Location:  Sanbonmatsu Castle in Tsuwano in the Kanoashi District of Iwami Province

Synopsis:  Sue Takafusa, a senior retainer of the Ōuchi clan, usurped Ōuchi Yoshitaka and installed Ōuchi Yoshinaga (from the Ōtomo clan) to serve as a puppet successor.  Yoshimi Masayori, a kokujin from Iwami Province loyal to Yoshitaka, sought to avenge the death of his lord by rebelling against the Sue.  This led to the siege of Sanbonmatsu Castle by the Ōuchi army while Masuda Fujikane led efforts to topple outlying castles.  Takafusa’s direct solicitation of kokujin in Aki, however, resulted in a break of relations between the Sue and Mōri clans.  The siege finally ended with a negotiated settlement on the condition that Masayori tender his son as a hostage to the Ōuchi.

Lord: Ōuchi Yoshinaga

Commanders:  Sue Takafusa, Masuda Fujikane

Forces:  Unknown

Losses:  Unknown

Commanders:  Yoshimi Masayori

Forces:  Unknown

Losses:  Unknown

The Siege of Sanbonmatsu Castle occurred from the third to eighth months of Tenbun 23 (1554).  The battle was waged between the Ōuchi army led by Ōuchi Yoshinaga, and his senior retainers, Sue Takafusa (later known as Sue Harukata) and Masuda Fujikane, against Yoshimi Masayori, the lord of Sanbonmatsu Castle in Tsuwano in the Kanoashi District of Iwami Province.


In 1551, after the death of Ōuchi Yoshitaka by Sue Takafusa (later known as Harukata) in the Tainei Temple Incident, members of the Ōuchi family who turned to the Ōtomo clan of Bungo Province in northern Kyūshū invited Ōtomo Haruhide to serve as the new lord of the Ōuchi clan under the name of Ōuchi Yoshinaga.  He was, in fact, a puppet ruler under the control of Sue Harukata, but Mōri Motonari along with kokujin, or provincial landowners, including Masuda Fujikane who had been under the command of the Ōuchi continued in service of Yoshinaga.

Those serving the Ōuchi included Yoshimi Masayori, a kokujin from Tsuwano in Iwami Province.  Masayori was a brother-in-law of Yoshitaka, having wed Yoshitaka’s older sister as his formal wife.  Masayori owed a large debt of gratitude toward the Ōuchi for his succession to the headship of the Yoshimi family.  Meanwhile, the Yoshimi and Sue clans experienced frequent conflict, becoming arch-rivals.  During the Tainei Temple Incident, Sue Takafusa directed the forces led by Masuda Fujikane to attack the territory of the Yoshimi clan.  As a result, since the time of the incident, Masayori stood in opposition to Takafusa.

Course of events


In the tenth month of 1553, Yoshimi Masayori rebelled with the aim of ousting the Sue clan.  Prior to launching the rebellion, around the fifth month of the same year, Masayori dispatched a retainer named Shimose Yorikane (Sakyō-no-jō) to request support from Mōri Motonari.  At this time, there is a commonly held theory that a secret pact was made between the Yoshimi and the Mōri, but there are no historical records to substantiate this arrangement which appears to be an embellishment of later generations.

Harukata directed his forces to eliminate Masayori, but suffered losses against Masayori who fought against the Sue under the banner of avenging the loss of his lord.  Hostilities first broke out at the Nosaka Pass at Kōsabara in Nagato Province, during which Shimose Yorisada and Hatano Shigenobu (retainers of the Yoshimi) repelled the Sue army led by Machino Takakaze.  While waiting for the snow to melt, Harukata planned a larger-scale attack against the Yoshimi, pressing Motonari and kokujin under his command to deploy.  Haurkata requested their deployment around the first month of the following year, but the Mōri did not make clear their intentions.  After growing impatient at the apparent disinterest from Motonari to deploy, at the end of the second month, Harukata sent a secret messenger to the kokujin in Aki Province to demand their deployment.

Deployment by Sue Harukata

On 3/1 of Tenbun 23 (1554), Sue Harukata deployed in service of Ōuchi Yoshinaga.  Others serving in the Ōuchi army included Era Fusahide, Naitō Takayo, Shirai Katatane, Nomi Katakatsu, Katsumada Moriharu, Waki Kanechika, Ikōga Ietomo, Kuba Katashige, Miyagawa Fusanaga, Miura Fusakiyo, and Machino Takaharu.

Yoshinaga established his main camp at Watarigawa Castle in Nagato while Harukata led a vanguard division to Motoyama Castle.

On 3/2, the forces attacked Kane Castle, an auxiliary to Sanbonmatsu Castle.  At Kane Castle, Hatano Shigenobu (the lord of the castle) and his son, Hatano Hidenobu, along with Yoshimi Norihiro and Shimose Yoshisada (who came as reinforcements), were holed-up.

Yoshika Yorisada and his son led a unit and set-up a camp a short distance away from Mount Katsu.  Harukata led the vanguard of the Ōuchi army including the Hironaka, Miura, and Machino forces and surrounded Kane Castle.  The natural terrain made the castle difficult to attack, and the defenders fought valiantly, but, owing collusion by a retainer named Tanaka Jirōbei, the castle fell the next day.  Hatano Shigenobu and his son, Hidenobu, along with Yoshimi Norihiro, were killed in action while Shimose Yoshisada and Yoshika Yorisada fled.

On 3/16, the Ōuchi army converged with forces led by Masuda Fujikane.  Meanwhile, Yoshinaga’s main camp moved to Motoyama Castle and engaged in attacks on numerous castles aligned with the Yoshimi, including Shika-ga-take, Wanibōyama, Hirayama, and Kushizaki castles.

Military strength

According to one account, a total of 50,000 forces from the Sue, Era, and Miura gathered for five months in Tsuwano.  This total, however, is quite high compared to the number of troops mobilized by the Ōuchi and Sue from Suō and Nagato provinces in other conflicts, such as 15,000 troops in the Ōuchi army for the First Siege of Gassantoda Castle, 5,000 Sue forces at the Tainei Temple Incident, and 20,000 combined forces from the Ōuchi and Sue at the Battle of Itsukushima.  In an Edo-period account, a total of 30,000 Sue forces opposed 1,000 defenders at Kane Castle.  Even if this is not completely fabricated, in view of the scale of Kane Castle, the number appears excessive.  According to a report on the history of Tsuwano, the Ōuchi and the Sue fielded a combined total of 20,000 soldiers.  Local historians cite 15,000 soldiers in the Ōuchi contingent (including 2,000 from the Masuda) and 1,200 soldiers in the Yoshimi army.

Siege of Sanbonmatsu Castle

On 3/19, the vanguard forces led by Sue Harukata began the siege of Sanbonmatsu Castle.  Those holed-up in the castle included locals from the village below the castle.  Harukata established a position on a mountain at an elevation of 420 meters looking down upon the castle from the south across the Tsuwano River.  Meanwhile, Harukata had Era Fusahide set-up a base to the north facing the rear entrance to the castle.

On 4/17, the Ōuchi army commenced an all-out assault on the castle, but the defenders succeeded in warding-off the attackers.  Thereafter, until 8/2, a total of twelve clashes occurred, but Sanbonmatsu did not fall to the besieging army.  Owing to fires associated with the fighting around the castle, surrounding shrines and temples, including the Washihara-Hachiman Shrine, burned down.

The defenders in nearby Shimose and Mitake castles repelled the attacking forces.  Shimose Castle, located on Mount Shimose on the border between the territories of the Yoshimi and the Masuda clans stood approximately ten kilometers to the north of Sanbonmatsu Castle, connected via a ridge line.  In an effort to isolate Sanbonmatsu Castle, Masuda Fujikane attacked Shimose Castle.  In addition to attacking the castle, Fujikane employed various tactics to pursue its capture.  At the end of the third month, he informed the defenders that Nagano Castle had fallen and urged them to surrender.  In the fifth month, Fujikane had a letter containing false information delivered to the defenders of Shimose Castle stating that the Mōri (backing the Sue) attacked Sakurao Castle, but fled in defeat following betrayals by the Kumagai, the Miyoshi, and the Kobayakawa.  In the eighth month, he communicated that four-way peace negotiations were proceeding among Sue, the Yoshimi, the Masuda, and the Amago.  The defenders, however, rejected these various scenarios.  Moreover, while holed-up in the castle, Masayori moved his main base to Shimose Castle to avoid the exposure of fierce attacks by the Sue army against Sanbonmatsu Castle.

Movements of the Mōri army and reconciliation

In Aki, at the beginning of the third month, Motonari learned of the secret letters and messengers serving Harukata.  These were the letters and messengers that Harukata sent to the kokujin, or provincial landowners, at the end of the second month in Aki.  These actions breached the promise that the kokujin in Aki would be governed by the Mōri so the Hiraga clan, who had pledged loyalty to the Mōri, apprehended a messenger.  This hastened the separation of Motonari from the Ōuchi and his move toward independence.  On 5/12 of Tenbun 23 (1554), the Mōri parted ways with the Ōuchi and Sue and rebelled, launching lightening attacks against castles in Aki that were aligned with the Sue.  This event is known as the Separation of Suō and Aki.  Harukata responded by assigning 3,000 soldiers to a retainer named Miyagawa Fusanaga and rushing them to Aki, but, on 6/5, these forces were defeated at the Battle of Oshikibata.

At the battle for Sanbonmatsu Castle, there is an account that Ninomiya Uchū and Itō Mototane (retainers of the Mōri) came running with a small unit as reinforcements to help build-up the defenses at Nakaara Castle.  However, in view of the situation between the time of the Separation of Suō and Aki on 5/12 and the Battle of Oshikibata on 6/5, the dispatch of reinforcements during this period is regarded as unlikely so it is surmised that no reinforcements were sent by the Mōri at this time.

Harukata leveraged groups opposed to the Mōri, including ikki forces and members of the security (naval) forces, to contain the Mōri, but while the main divisions of the Ōuchi and Sue were pinned down in Sanbonmatsu Castle in Iwami, these clans faced difficult circumstances as Motonari increased his control over Aki Province.  Meanwhile, Yoshimi Masayori and those holed-up with him confronted dwindling provisions as a result of the prolonged siege.  This led to settlement discussions between the Ōuchi and Sue on one side and the Yoshimi on the other.  On 9/2, a settlement was reached on the condition that Masayori send his son, Kameōmaru (later known as Yoshimi Hiroyori) as a hostage to Yamaguchi.  In addition to those at Sanbonmatsu Castle, the defenders of Shimose and Mitake castles held-out and avoided capture of their castles.


After lifting the siege, the Ōuchi army returned to Yamaguchi.  Harukata promptly undertook preparations to oust Motonari, establishing Iwakuni, a town on the far eastern side of Suō, as a base for invading Aki.  Motonari, however, had persuaded Era Fusahide and Kuba Katashige to collude with him to prevent an attack by the Ōuchi.

In 1555, after the Mōri prevailed against Harukata at the Battle of Itsukushima, Yoshimi Masayori acted in concert with Motonari in the Subjugation of Bōchō.  After recovering his son, Kameōmaru, from the Ōuchi, along with Hirayama and Kane castles in his former territory, Masayori kept movements of the Masuda clan in check while attacking Yamaguchi.  Having made significant contributions to the Subjugation of Bōchō, Masayori came under the command of the Mōri and was awarded the Abu District in Nagato Province.