The Battle of Shimanto-gawa River (四万十川の戦い)

The Battle of Shimanto-gawa River, which is also referred to as the 'Battle of Watari-gawa River,' was a battle that confirmed the unification of Tosa Province (Kochi Prefecture) by Motochika CHOSOKABE in 1575.

The Process leading to the Battle
The Tosa Ichijo clan was an influential family and a branch of Gosekke, which was the Northern House of the Fujiwara clan, and ruled Hata District in the western part of Tosa (what is now the area around Shimanto City) during the Sengoku period (period of the warring states). With their distinguished family lineage, the clan subjugated the local clans and had a strong influence over the western part of Tosa where they ruled peacefully. However as the unification of Tosa by Motochika CHOSOKABE became increasingly realistic, the local clans who were in the area east of the Shimanto-gawa River turned to Motochika for alliance, and as such, the area where the Ichijo clan could exert their influence was contained within the areas downstream and west of the Shimanto-gawa River. In February 1574, the vassals of the Ichijo clan staged a coup, and the family head Kanesada ICHIJO was driven out and escaped to Bungo Province where his wife's family, the Otomo clan, was.

Hata District thus came to be ruled by Motochika CHOSOKABE without bloodshed. The following year in 1575, however, Kanesada Ichijo who came back from Kyushu raised an army in Uwajima City, Iyo Province, and returned to his home base Nakamura City with an entourage of his old vassals. Then the local clans who felt indebted to the Ichijo clan joined the army one after another, and the number of troops rose to 3,500 quickly. Kanesada established headquarters in the Kurimoto Castle on the west bank at the mouth of the Shimanto-gawa River, and prepared for the enemy's attack by planting stakes and utilizing the geography. He knew that the army of Chosokabe would arrive sooner or later.

The Process of the Battle
As the Ichijo army provoked the enemy by attacking villages east of the Shimanto-gawa River and the castle town of the Nakamura-jo Castle, Motochika CHOSOKABE arrived on the east bank of the Shimanto-gawa River with the army 7,300 strong after a mere three days. Although there was the system of Ichiryo gusoku in Tosa at that time, which allowed local cultivators to arm themselves, there was a standing army, and as such, when the Chosokabe clan advanced with a large army within a short time, the Ichijo clan with a small army was truly astounded. This is a telling episode about the efficiency of the Ichiryo gusoku system.

The battle between the two armies stationed on the east side and west side of Shimanto-gawa River was started by the provocation of the Chosagabe army. When the first unit of the Chosogabe army advanced head-on into the river, the Ichijo army retreated in order to attack the enemy with arrows and bullets as they reached their side of the river. As they were overwhelmed by the sheer number, there was not an option for them to attack.

At the moment the Chosokabe army took the opportunity to send the second unit, the cavalry led by Norishige FUKUDOME, which started to run upstream. The Ichijo army panicked seeing the enemy's move to attack from upstream where there were no stakes to protect them, and sent some groups upstream to chase the Chosogabe army, which caused their army to scatter. Taking the opportunity as the Ichijo army became divided, Motochika CHOSOKABE ordered the rest of his army to cross the river.

The Ichijo army, which scattered their small army, did not have capacity to counter the head-on attack of the enemy force of more than double in number. Further, the Ichijo army was a quickly assembled army of inconsistent soldiers and there was no unified chain of command. There was no way that they could squarely fight with the veteran troops who had survived the various battles in central Tosa for a long time, and the Ichijo army collapsed immediately and was routed. While the Ichijo army suffered a loss of a several hundred soldiers, there was no substantial damage to the Chosokabe army. The Battle of Shimanto-gawa River, which was the deciding battle for the ruling of Tosa, lasted only half a day. They even carried out kubijikken (identifying of severed heads) before the sun had set over the Nakamura Plain.

After the Battle
Kanesada Ichijo, who barely escaped with his life from the battle, did not have another opportunity for a revenge battle, and he died at the age of 40 after living in retirement for 10 years. Motochika CHOSOKABE, on the other hand, unified Tosa Province, and then went on to dominate Shikoku. His attempt, however, was interrupted by the invasion of Hideyoshi TOYOTOMI merely a few weeks after he dominated Shikoku in 1585.