Battle of Shimantogawa
Date: Tenshō 3 (1575)
Location: Shimanto River in Tosa Province
Synopsis: The Tosa-Ichijō were a family of noble lineage having ties to the Imperial Court in Kyōto. In the era of Ichijō Kanesada, the family witnessed a decline in their influence and a rebellion by retainers causing Kanesada to flee for a period to Kyūshū. Later, he returned to Tosa Province and, with the support of former retainers, sought to recover his territory. Chōsokabe Motochika, the head of the most powerful clan in Tosa, confronted the Ichijō across the Shimanto River, and, after a brief and lop-sided battle, the Ichijō fled in defeat. This event represented the final step in the unification of Tosa by the Chōsokabe.
The Battle of Shimantogawa occurred in Tenshō 3 (1575) between the Chōsokabe and Tosa-Ichijō clans in Tosa Province. This battle marked the unification of Tosa Province by Chōsokabe Motochika. This is also referred to as the Battle of Watarigawa.
The well-known Ichijō family were one of the Five Regent Houses (along with the Konoe, the Takatsukasa, the Kujō, and the Nijō) of the Fujiwara-Hokke, entitled to serve as regents and advisors to the Imperial Court of Kyōto dating back to the twelfth century. In 1468, Ichijō Norifusa, the prior kanpaku, or Chief Advisor to the Emperor, sought to avoid the chaos of the Ōnin War by coming from Kyōto to reside in the Hata manor of western Tosa where the family had landholdings, serving as provincial governors. Owing to the noble heritage of the family, surrounding families obeyed them while the Ichijō exercised their power through peaceful means. However, around the time of the Eiroku era when Ichijō Kanesada served as its final head, the Ichijō clan engaged in battle against Kōno Michinao (through intervention of the Mōri) and witnessed threats against its territory as the Chōsokabe rose to prominence. The influence of the Ichijō clan in Tosa began to wane.
Kanesada joined forces with Aki Kunitora of eastern Tosa to resist Chōsokabe Motochika, but, after Kunitora was decimated at the Battle of Yanagare, gōzoku located to the east of the Shimanto River surrendered to the Chōsokabe one after another. As a result, the sphere of influence of the Ichijō clan was limited to the area to the west of the Shimanto River basin. After Kanesada began to indulge in pleasures and gradually lose interest in governing, he killed a senior retainer named Doi Sōzan for attempting to admonish his lord for misbehavior, thereby losing the support of his retainers. In the second month of 1574, a rebellion by his retainers led to his ouster from Tosa and he fled to Bungo Province in Kyūshū to seek refuge with the Ōtomo clan who were the original family of his wife. This series of events also reflected the effects of rumors and scheming on the part of Motochika.
The Hata District came under the governance of the Chōsokabe with almost no fighting, but, in 1575, Kanesada returned from Kyūshū with the aim of recovering his former territory in western Tosa whereupon he raised arms in Iyo-Uwajima. With the support of former retainers, he returned to his original base at Nakamura in Tosa. His presence prompted dogō, or small-scale landowners who felt loyalty to the Ichijō family to return to their service, reaching a military force of 3,500 troops. This made a military conflict between the Ichijō and the Chōsokabe inevitable. On the western shore of the mouth of the Shimanto River, from Kurimoto Castle, Kanesada installed pickets at the Shimanto River and prepared to intercept the enemy forces by taking advantage of the local topography.
Course of events
After the Ichijō caused a provocation by attacking a village and the town below Nakamura Castle to the east of the Shimanto River, just three days later, Chōsokabe Motochika led 7,300 troops to the eastern shore of the Shimanto River. Armies in this period did not typically have a reserve corps, so the Ichijō were surprised to see the appearance of such a large contingent in a short time. This may have been facilitated by the end of the planting season and provided an example of the value of the ichiryō-gusoku system conceived by the Chōsokabe to field armies comprised of troops who split their time between farming and military service.
The two armies confronted one another from the east and west shores of the Shimanto River. First, the First Division of the Chōsokabe forces attempted to traverse the river from the front. Having fewer forces than the Chōsokabe, the Ichijō pulled back and rained down arrows and arquebus fire on them. Fukutome Yoshishige then immediately headed north with a unit from the Second Division of the Chōsokabe, going upstream to get around the shoreline that the Ichijō had blocked with pickets. Fearing a pincer attack from two directions, the Ichijō divided their forces with some heading upstream in pursuit of the forces led by Yoshishige. Without losing the opportunity, Chōsokabe Motochika ordered his entire army to traverse the river en masse.
With respect to the Ichijō, the inferior number of soldiers became further dispersed, while confusion led to a breakdown of command. The Ichijō did not have the capacity to counter a frontal assault by the Chōsokabe having a significantly greater number of troops, leading to a sudden collapse of their army. As the Chōsokabe forces gave chase, over 200 Ichijō soldiers were killed while fleeing, whereas the Chōsokabe incurred only minimal losses. In this battle at the Shimanto River, the struggle for control over Tosa Province was swiftly determined. Before nightfall, the Chōsokabe had already completed their inspection of the heads of fallen enemy soldiers.
In this battle, Kanesada fled and, after living in seclusion in the area of the Seto Inland Sea, died at the age of forty-three. Meanwhile, having unified Tosa Province, Chōsokabe Motochika continued to engage in many battles with the aim to garner control of all of Shikoku. Around 1585, his territory encompassed most of the island. Soon thereafter, however, he was subject to the Invasion of Shikoku by Hashiba Hideyoshi, surrendering to the invading forces and becoming a daimyō in control only of Tosa Province.