Saturday, October 4, 2014

Oko Castle -Castle of regional hero who united Shikoku island-

Oko Castle

-Castle of regional hero who united Shikoku island-



Name: Oko castle /Okou castle (Oko-jo)
Place: Okocho Nankoku city, Kochi
Type: Hill Castle
Built: 13th century, expanded in 16th century
Remaining remnants: Stone walls, clay walls and moats

Brief History

Oko castle (岡豊城) is located at Oko mountain, a mountain of 100 meter height at the north edge of Kochi plain and stands aside Kokubugawa river flew into Tosa bay. 

Kochi plain is divided into three parts, it mean eastern part of Mononobegawa river area, middle part of current central Kochi city and western part of Niyodogawa river area. Historically the center of Tosa country (Kochi prefecture) has located at eastern part of Kochi plain, and the site of Oko castle is applicable to the border of eastern part and middle part. The mountainous road from Awa country (Tokushima prefecture) also passes through this area, and Oko area is an important place of communication.

Chosokabe clan in medieval era

Oko castle was built by Chosokabe clan as their residence in medieval era. The origin of Chosokabe clan is unknown but it is said that they are descendant of Hata clan, an immigrant from Baekje country of ancient Korea and originally named as Sokabe clan. Sokabe clan was appointed as local retainer of Tosa country by Kamakura shogunate and entered the country in 13th century. Sokabe clan grew their territory by branch houses, and to distinguish main stream of the clan, Sokabe clan changed their surname as Chosokabe clan, using the name of their residence.

In Muromachi era, Hosokawa clan, a branch house of Muromachi shogunate, was appointed as a governor of Tosa country, along with Awa country and Sanuki country (Kagawa prefecture). Chosokabe clan became an important retainer of Hosokawa clan and supported their administration. But Hosokawa clan became the participant of the battle of Onin (1467-1477) and significantly lost its power and authority. At that moment Ichijyo clan, one of the highest class noble of Kyoto and had territory at the west end of Tosa country, escaped war-torn Kyoto and came to Tosa country in 1468. 

In 1507, due to its internal conflict, Hosokawa clan could not keep Tosa country and left. Tosa country was governed by alliance of seven major local lords such as Motoyama clan, Kira clan or Chosokabe clan, nominating Ichijyo clan as their nominal leader. Chosokabe clan gradually expand their power under this situation, but this evoked antipathy of other lords. Finally in 1508, alliance of large lords attacked Oko castle, and Kanetsugu Chosokabe (?-1508) who was the leader of Chosokabe clan, killed himself. Chosokabe clan once lost the power.

Leader called as wild tiger

Kunichika Chosokabe (1504-1560), the eldest son of Kanetsugu, left the castle and saved by Ichijyo clan. Later Kunichika recovered Oko castle and his territory under coordination of Ichijyo clan, and seek revenge. At first Kunichika made peach with Motoyama clan, the strongest rival of Chosokabe clan by marriage. Then Kunichika defeated small lords and grew his territory, and send his sons to other local lords such as Kosokabe clan or Kira clan as adopted son and dominated them. 

In 1555, the final battle between Kunichika and Motoyama clan began. In 1560 Kunichika defeated Motoyama clan with less soldiers at the battle of Nagahama, and captured Urado castle, an important fortress faced Urad gulf. Due to his achievement Kunichika was nicknamed as "Wild Tiger", but just after the battle Kunichika died in ill and his eldest son Motochika Chosokabe (1539-1599) succeeded the leader position.

Unite of Tosa country

Although the son of brave lord, Motochika grew mild and quiet, and was said like princess. Motochika experienced the first battle at the battle of Nagahama in 21 years old, and it was quite late at that period. But Motochika fought bravely and made achievement, and showed his talent to surrounding people.

Motochika who succeeded Chosokabe clan lead his half pheasant soldiers named "Ichiryo Gusoku" and continued the operation against Motoyama clan. In 1563 Motochika occupied Asakura castle, the residence of Asakura clan, and substantially defeated them. Next year Motochika also beated Aki clan at the east part of Tosa country and grasped that area.

At the west part of Tosa country Ichijyo clan still exist, but they lost their power by defeat by Kono clan, the governor of Iyo country (Ehime prefecture) supported by Mouri clan in 1568. Utilizing this chanse Motochika suppressed Ichjyo clan and expelled non obedient leader Kanesada Ichijyo (1543-1585) in 1573. Kanesada tried to revenge to Motochika and returned to Tosa country, but Motochika beat Kanesada again at the battle of Shimantogawa river in 1575, and now completely united Tosa country.

Relationship with central power

Motochika who became the governor of Tosa country next aimed at other countries of Shikoku island. At that time, Sanuki country and Awa country were held by Miyoshi clan and Iyo country was managed by Kono clan under influence of Mouri clan, a strong warlord of Chugoku region. At first central ruler Nobunaga Oda (1534-1582) fought with Miyoshi clan, Motochika at first made friendship with Nobunaga through Mitsuhide Akechi (1528-1582), an important retainer of Nobunaga. Miyoshi clan lost their power by the battle against Nobunaga, and Motochika could expand to major part of Awa country and Sanuki country. Motochika also fought with Kono clan at Iyo country.

But around 1580, Nobunaga turned to be cautious about expansion of Motochika and began to suppress them. Nobunaga changed his representative in Shikoku island from Mitsuhide to Hideyoshi Hashiba (1537-1598, later Hideyoshi Toyotomi) and let him to support remaining Miyoshi clan. Mitsuhide lost his face by this fact and this could be one cause of the incident of Honnoji, a coup d'etat against Nobunaga by Mitsuhide in 1582.

In 1582, Nobunaga ordered his third son Nobutaka Oda (1558-1583) and his general Nagahide Niwa (1535-1585) to across to Shikoku island and subjugate Motochika. This expedition army was about to start in June but the incident of Honnoji occurred thus this attempt was cancelled. Motochika barely escaped this crisis.

Residence of ruler of Shikoku island

During the confusion after the incident of Honnoji, Motochika accelerated his campaign to unite Shikoku island. In 1582 Motochika beated Sogo clan at the battle of Nakatomigawa river, expelled Sogo clan and Miyoshi clan and seized most part of Awa country. Hideyoshi sent his general Hidehisa Sengoku (1552-1614) to Hiketa castle (Kagawa prefecture) as a restraint to Motochika, but Motochika beat Hidehisa and let him return. Further Mouri clan was exhausted by the battle against Oda clan, Motochika suppressed Kono clan and let them subordinate to Motochika. Now Motochika once virtually completed unite of Shikoku country which was his ambition.

Along with the expansion of Chosokabe clan, Oko castle was improved as main residence. The main part of Oko castle consist of four terraces spread along with the ridge, and even though not large entrance into the castle was guarded by composite gate and guarding forts. Basically each terrace are separated by clay walls but stone walls are partially used. Suitable for the residence of the ruler of Shikoku island, there were large building covered by roofing blocks, and next hill of the castle was also used a front fort of the castle.

Later Motochika was defeated by Hideyoshi Toyotomi at Shikoku campaign in 1585 and his territory was decreased to only Tosa country. At that year Motochika newly built Otakayama castle (current Kochi castle) and reformed Urado castle (Kochi city) and moved his residence to there, thus Oko castle was abolished then. Now the castle site became the park, and it small but strong shape of the castle is the very thing of the image of Motochika.

Continue to Urado castle


40 minutes walk from JR Shikoku Dosan-sen line Tosa-Otsu station. 15 minutes drive from Kochi-Jidoshado Expressway Nankoku interchange. Just at the next of Kochi Prefectural Museum of History.

Related Castles

Urado Castle -Downfall and disappearance of regional ruler-
Kochi Castle -White elegant buildings on secure stone wall-

Pictures (click to enlarge)

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