The Battle of Nagaragawa occurred in the fourth month of Kōji 2 (1556) at the Nagara River in Mino Province.  The conflict was waged between Saitō Dōsan and his eldest son, Saitō Yoshitatsu.

Reasons for the battle

In 1542, Saitō Dōsan replaced the prominent Toki clan as the provincial lord of Mino.  In 1554, he transferred Mino to his eldest (illegitimate) son, Saitō Yoshitatsu and retired.  Dōsan, however, gradually viewed Yoshitatsu as a fool and regarded Yoshitatsu’s younger brothers, Saitō Magoshirō and Saitō Kiheiji, as clever.  Further, he gave Kiheiji the name of Isshiki Uhyōe Taifu.  While disregarding Yoshitatsu, Dōsan assigned the prominent Isshiki surname and title to Kiheiji.  Meanwhile, the two younger brothers became arrogant and treated Yoshitatsu with contempt which led to a deepening divide between Dōsan and Yoshitatsu.  In the tenth month of 1555, Yoshitatsu feigned illness and holed-up in Inabayama Castle.  Yoshitatsu determined that Dōsan would remove him from the line of succession and designate one of his younger brothers as his successor so he set about to devise countermeasures.

Prelude

On 11/22 of Kōji 1 (1555), Yoshitatsu took advantage of an opening when Dōsan was away at this private residence in the foothills of Inokuchi.  Yoshitatsu sent his uncle, Nagai Michitoshi, to Yoshitatsu’s two younger brothers, Magoshirō and Kiheiji, to call them to his side, stating “I have a serious illness so it is only a matter of time.  I would like them to come to share a message.”  Michitoshi then executed a plan, placing a sword in the adjacent room and had the two brothers follow his lead to place their swords down.  He then served saké across a table and after becoming intoxicated, they were slayed by Hineno Hironari with a sword.  After having his brothers murdered, Yoshitatsu sent a messenger to Dōsan inform him of the event.  Surprised at hearing the news, Dōsan hurriedly gathered soldiers, burned down the town below the castle, and fled.

After traversing the Nagara River, Dōsan fled to Ōga Castle in Yamagata.  The following year, after the snowmelt, tensions rose as the two sides prepared for an imminent battle in the spring.

Course of events

On 4/18, Dōsan first set-up a base on Mount Tsuru.  His son-in-law, Oda Nobunaga, of Owari, traversed the Kiso and Hida rivers by boat and established a base at Tojima and Tōzōbō in Ōyoshi.

Around 8:00 AM on 4/20, Yoshitatsu’s army advanced to the southern shore of the Nagara River whereupon Dōsan’s army descended Mount Tsuru and moved to the northern shore of the river.  Thereafter, the two armies engaged in a violent clash.

Owing to the course of events as Dōsan usurped the Toki clan to become the provincial lord of Mino, a majority of the family members including those of the Western Mino Group of Three supported Yoshitatsu.  Yoshitatsu enjoyed an overwhelming numerical advantage by fielding 17,500 troops compared to 2,700 troops in Dōsan’s army.

The battle began with a charge by 5,000 soldiers Yoshitatsu’s vanguard division led by Takegoshi Dōchin.  After adopting a circular formation, the members of the division rushed across the Nagara River and pressed toward Dōsan’s main base, cutting through enemy forces.  As the scene descended into a melee, Dōsan directed his retainers to victory and compelled the Takegoshi forces to flee in defeat.  Dōchin was killed by Dōsan’s forces.  Yoshitatsu responded by leading a contingent across the river and establishing another base.  At this time, Nagaya Jinemon from Yoshitatsu’s forces engaged in a one-on-one duel against Shibata Tsunouchi in Dōsan’s army.  After Tsunouchi slayed Jinemon, the two armies charged one another.

From the onset of hostilities, Dōsan lacked the forces needed to gain the upper hand in the battle while Yoshitatsu’s forces pressed forward.  Dōsan’s forces collapsed.  Nagai Tadazaemon Michikatsu (Inoue Michikatsu), a retainer of the Saitō, grappled with Dōsan seeking to capture him alive so he could take him in front of Yoshitatsu.  At this moment, however, Komaki Genta (Michiie) intervened and cut Dōsan’s lower leg, pushed him down, and took his head.  This upset Michikatsu who then sliced Dōsan’s nose as evidence that he grappled Dōsan first, placed it in his pocket and then left the scene.  Owing to the death of Dōsan, the battle headed toward an end.  Nobunaga headed toward the battle to serve as a rear guard but did not arrive in time.

Aftermath

During the inspection of heads of fallen enemy soldiers, Dōsan’s head was delivered.  At this time, Yoshitatsu declared that it was a crime arising from his own immorality.  He is said to have then entered the priesthood and adopted the name of Hanka.   This is the name of an individual who, during the era of the Tang dynasty (618 to 907) in China, murdered his father as a result of unavoidable circumstances.  Per the Shinchō-kōki, Yoshitatsu used this name as a reflection of his own situation.  The veracity of the legend associated with Hanka, however, is not confirmed.  Moreover, Yoshitatsu used this name prior to the date when his killed his father.  According to one account, he issued a prohibition to the Mie Temple under the name of Hanka in the twelfth month of 1555.  Therefore, the theory that Yoshitatsu adopted this name to assuage his guilt after the inspection of heads including that of his father appears erroneous.

Riding the momentum of their victory at the Nagara River, members of Yoshitatsu’s army finished the inspection of heads and then directed soldiers toward Nobunaga’s base at the gateway to Ōyoshi.  The two armies violently collided on the riverbed in Ōyoshi.  Among Nobunaga’s forces, Yamaguchi 取手介 and Hijikata Hikosaburō were killed in action.  Mori Yoshinari engaged in a skirmish with Sengoku Mataichi from Yoshitatsu’s army and pulled-back after sustaining a cut to the knee while atop a horse.  The sacrifices made by these individuals was helpful in sparing time for the withdrawal of other forces.

Amidst these circumstances, Nobunaga was informed that Dōsan had been killed so after sending the porters and horses to the back of the line, he said that he would take-up the rear guard.  He then had all of the soldiers retreat across the river and then he remained behind with one boat.  When members of the cavalry in Yoshitatsu’s army came to the edge of the river, Nobunaga fired his arquebus.  The cavalry abandoned efforts to cross the river and Nobunaga was able to withdraw.

The death of Saitō Dōsan also had consequences for neighboring Owari Province.  Oda Ise-no-kami Nobuyasu, the head of the Iwakura-Oda family governing the four upper districts of Owari acted in concert with Yoshitatsu, setting fire to villages in the Shimoyuki township near Kiyosu.  Nobunaga then invaded the territory of the Iwakura-Oda family and burned down the area near Iwakura.  Meanwhile, the Shobata-Oda family (Danjō-no-tada family) governing the four lower districts of Owari aligned with Yoshitatsu and Nobuyasu to defect from Nobunaga with the aim of backing his younger brother, Oda Nobuyuki (Nobukatsu), causing further turmoil.  This finally escalated into a succession struggle in the Shobata-Oda family.

After having killed his father, Yoshitatsu suddenly died five years later in 1561.  Yoshitatsu’s son, Saitō Tatsuoki, inherited the headship of the clan, but fell to the invasion by Oda Nobunaga of Owari and was ousted from Mino.  Later, he went to the Asakura clan of Echizen to seek help and continue resisting the Oda but was then killed in action at the Battle of Tonezaka in the eighth month of 1573, shortly before the Siege of Ichijōdani Castle that decimated the Asakura clan.  According to other theories, Tatsuoki continued to survive.

Within the Oda family, Nōhime’s younger brother, Saitō Toshiharu, inherited the Mino-Saitō clan and her older brother, Saitō Toshitaka served as a senior retainer.

Notes

There is a commonly known theory that Yoshitatsu was the natural son of Toki Yoriaki, the prior military governor of Mino who was usurped by Dōsan.  This is based on the assertion that Yoshitatsu’s mother, Miyoshino, was pregnant with Yoshitatsu before becoming a consort of Dōsan.  This is noted in genealogical records of families from Mino compiled during the Edo period so the validity of this theory is uncertain.  One scholar criticized existing theories regarding the succession from Dōsan to Yoshitatsu as well as Dōsan’s death in battle.  Noting the lack of documents issued by Dōsan in Mino, he concludes that Dōsan was forcibly removed by senior retainers opposed to his neglectful governance of the province.  The year after his ouster, Dōsan raised arms at the Battle of Nagaragawa in a bid to reclaim the headship of the clan.

According to the authenticated biography of Oda Nobunaga known as the Shinchō-kōki, Dōsan initially set-up his main base at Sagiyama Castle, but the prevailing view is that he was based on Mount Tsuru.

In this battle, the Akechi clan joined forces with Dōsan which led to an attack by Yoshitatsu on their base at Akechi Castle.  There is a theory that Akechi Mitsuhide narrowly escaped and began life as a rōnin, or wandering samurai.

Dōsan was pursued by former retainers including Nagai Michikatsu, Komaki Michiie (Genta), and Hayashi Mondo.  While being grappled down, his lower leg was cut and nose sliced.  He was respectfully buried by Michiie.

Reinforcements from the Oda army did not arrive in time.  After converging with remnants of Dōsan’s army including Saitō Toshiharu (the youngest son of Dōsan), the forces began to withdraw but were pursued by the Saitō army.  Nobunaga himself served in the rear guard, halting the pursuing forces with fire from the latest arquebus and enabling the forces to withdraw that day.

During the height of the confrontation at the Nagara River, Dōsan drafted a document to convey Mino Province to Nobunaga.