Sunday, October 25, 2020

Kosuiji Castle -Notable castle of noble family-

Kosuiji Castle

-Notable castle of noble family-



Name: Kosuiji Castle (Kosuiji-jo)
Place: Futsukamachi Shiwa town, Iwate
Location: 39.56547545734949, 141.17298000657811
Type: Mountain Castle
Built: 14th century?
Remaining remnants: Clay walls and dry moats 

Brief History

Kosuiji castle (高水寺城) is located over Shiroyama hill, one of about 80 meter height from hillside at the side of Kitakami-gawa river in the north part of Shiwa town. As the hill is an independent one prominent at flat area, from castle hill both of Morioka area at northward and Hanamaki area at southward is well seen.

Currently Shiwa providence is limited to the territory of Shiwa town, but formerly Shiwa providence included current Yahaba town and southwest part of Morioka city. Now castle area is at the north edge of Shiwa town, but formerly it existed at the center of Shiwa providence.

At 5 kilometer north from castle site there was Tokutan castle (Iwate prefecture), an ancient military base built by the Imperial Household in 9th century. Contrary to this, at 3 kilometer south of castle site, Hizumenotachi castle that was a second important base of Oshu Fujiwara clan next to Hiraizumi city. Between castle site and Hizumenotachi castle there might be providential office, thus this area had been the center of providence for long time.

Origin of Shiba clan

Precise year is unknown but Kosuiji castle might be built by Kosuiji Siba clan in 14th century. Shiba clan was originally a descendant of Ieuji Ashikaga (?-?), who was the eldest son of Yasuuji Ashikaga (1216-1270) but left the mainstream of the clan to his younger brother Yoriuji Ashikaga (1240-1262).

Ieuji Ashikaga achieved the territory of Shiwa providence originally held by Ashikaga clan, and indirectly managed Shiwa area from their original territory. At the fall of Kamakura Shogunate in 1333, Takatsune Ashikaga (1305-1367) who was a descendant of Ieuji Ashikaga followed Takauji Ashikaga (1305-1358), the leader of Ashikaga clan, and contributed to the establishment of Muromachi Shogunate.

Among the conflict between Muromachi Shogunate and the South Court, Tohoku region was managed by Akiie Kitabatake (1318-1338), the general commander of the South Court. To compete with the South Court army, Takauji Ashikaga sent Ienaga Shiba (1321-1338), the eldest son of Takatsune Ashikaga, to Shiwa providence to restrain Akiie Kitabatake from backward.

Akiie Kitabatake made two time long expeditions from Tohoku region toward Kyoto city in 1335 and 1338, and Ienaga Shiba was broken two times and died in the second battle at Kamakura city. But soon Akiie Kitabatake also died during second campaign, then the descendant of Ienaga Shiba could survive as the lord of Shiwa providence.

Prosperity of Shiba clan

At Muromachi Shogunate, the main family of Shiba clan stem from Yoshiyuki Shiba (1350-1410), the younger brother of Ienaga Shiba, was appointed as “Kanrei” position which was the highest class retainer of Shogunate. Shiba clan, Hatakeyama clan and Hosokawa clan which were relatives of Ashikaga clan had qualification to be “Kanrei”, but due to its origin Shiba clan was the highest among three clans.

As Tohoku region was an original territory of Shiba clan, Shiba clan thought important of the region. Iekane Shiba (1308-1556), the younger brother of Takatsune Shiba, was appointed as general governor of Tohoku region and moved to Nakashinden castle (Miyagi prefecture). Iekane Shiba became the origin of Osaki clan, and his second son Keneyori Shiba (1316-1379) moved to Dewa province (Yamagata prefecture) and became the origin of Mogami clan.

Shiba clan seized Tohoku region through Kosuiji Shiba clan at north, Osaki clan at south and Mogami clan at west. Kosuiji Shiba clan at first lived at Kosuiji temple near from Shiroyama hill, but later built defense fort at Shiroyama hill for security reason and then moved there. Kosuiji Shiba clan itself was not a large lord but being supported by the authority of Shiba clan Kosuiji castle was expanded into huge one.

Structure of Kosuiji castle

Central area of Kosuiji castle is an oblong shaped one of about 120 meter long and 50 meter wide at the peak of the hill. At the north of central area, large terraces such as Ukyo-Yashiki or Hime-Goten were built along with the ridge. At the south of central area, ahead of dry moat, another large area called as Wakatono-Yashiki watched southward of the castle.

Surrounding these core areas, three layers of terraces were built at the slope of the hill.
As the eastward of the hill is a sheer cliff faces Kitakami-gawa river, gates into core area are built at western line. Westward line of the hill is protected by the line of dry moat, and outside of dry moat there was a castle town still keeps the shape of the road and obstacle shaped ground of houses.

At the southwest of the hill, there are two outer forts named as “Mukaiyama” and “Kichibe-Yakata”, both exceeds 100 meter long. There were ruins of several fort which might be used as the relatives of Shiba clan, and total size of the castle is about 1000 meter long and 600 meter wide. The size of hilltop castle exceeds 600 meter long and 400 meter wide, and size and structure of the castle is prominent among medieval castles of Iwate prefecture.

Decline of Shiba clan

Shiba clan prospered as the highest class retainer of Muromachi Shogunate in the former half of 15th century, but in the middle of 15th century Shiba clan lost leaders in youth and this brought internal conflict to the clan. Besides, Shiba clan had its territory at distant areas such as Owari province (Aichi prefecture) or Echizen province (Fukui prefecture), it could not acquire the economic development in Kinki region different from Hosokawa clan and Hatakeyama clan that held territories at Kinki region.

In the beginning of 16th century, Shiba clan lost Echizen province by the rise of deputy governor Asakura clan, and also face the rise of Oda clan at remaining Owari province (west half of Aichi prefecture). Finally Shiba clan became the nominal governor above Oda clan, then revolted against Nobunaga Oda (1534-1582) and was expelled then the history of Shiba clan as the important retainer of Oda clan had ended.

At Tohoku region, each families of Shiba clan also faced the rise of local warlords such as Date clan and Nanbu clan since the beginning of 16th century. Osaki clan lost its power from the conflict with its fatal rival Kasai clan and rebel of retainers then subordinated to Date clan. 

Mogami clan which was the lord of Yamagata castle (Yamagata prefecture) was also suppressed by Date clan and once was controlled, but Yoshimori Mogami (1521-1590) and his son Yoshiaki Mogami (1546-1614) left Date clan and could transform into a large independent warlord of Yamagata basin.

Struggle of Kosuiji clan for survival

Kosuiji Shiba clan also suffered from southward expansion of Nanbu clan. In the beginning of 16th century Nanbu clan already fought at Tono area or Mizusawa area at southward of the territory of Kosuiji Shiba clan, then Nanbu clan overwhelmed Kosuiji Shiba clan but did not attack considering the punishment from Muromachi Shogunate.

In 1540, Nanbu clan intruded into Shizukuishi area between Morioka area and Akita prefecture, and expelled Tozawa clan which was the lord of Shizukuishi area to Kakunodate area of current Akita prefecture. Looking at this opportunity, Kosuiji Shiba clan seized Shizukuishi area from Nanbu clan, and placed their relative at Shizukuishi castle (Iwate prefecture).

Kosuiji Shiba clan kept these territories for a while, but being suppressed by Nanbu clan then agreed with Nanbu clan accepting Yagoro Kunohe (?-?), the son of Masazane Kunohe (1536-1591) who was an important retainer and vanguard of Nanbu clan. But Kosuiji Shiba clan broke with Yagoro Kunohe and expelled him to Nanbu clan.

Fall of Kosuiji Shiba clan

Kosuiji Shiba clan attacked Nanbu clan but suffered severe defeat before the counter attack of Nanbu clan, then lost Shizukuishi area in 1586. Muromachi Shogunate and Shiba clan already disappeared then Nanbu clan further attacked Kosuiji Shiba clan. In 1588 Iwashimizu clan which was the retainer of Kosuiji Shiba clan revolted, and utilizing this opportunity Nanbu army attacked Kosuiji castle.

Retainers of Kosuiji Shiba clan did not help the lord, then Akinao Shiba (1548?-1597?), the last leader of the clan, left Kosuiji castle then the clan ended its history as the warlord. Yagoro Kunohe renamed to Yasuzane Nakano was appointed as the commander of Kosuiji castle also renamed to Koriyama castle.

Nanbu clan which became a feudal lord under Toyotomi government and Edo Shogunate built Morioka castle (Iwate prefecture) as its main base since 1597, but due to the military operations at the battle of Sekigahara or continuous floods the construction of Morioka castle did not progress well.

Temporal use by Nanbu clan and afterward

Nanbu clan used Sannohe castle (Aomori prefecture) or Kunohe castle (Iwate prefecture) as temporary main bases, but they located at the north border of the territory and it was necessary to reside at southern area. Nanbu clan moved temporal base to Kosuiji castle, and the castle might be renovated into modern castle with stone walls.

In 1633, whole part of Morioka castle had completed then Nanbu clan moved from Kosuiji castle. Kosuiji castle was kept as a branch castle, but was abolished in 1668. The buildings of the castle were moved to Morioka castle, and stones of stone walls were used for river construction of Kitakami-gawa river but stones slightly remain around gate area.

Now no building remains but structure of the castle well remains over the hill in spite of change from park construction. Kitakami basin was included into Mutsu province and its governor was Date clan resided at Fukushima area, but the size and structure shows Kosuiji Shiba clan was equivalent to the governor of province. Kosuiji castle and the name of Shiba clan were too much for Nanbu clan and were finally abolished.


30 minutes walk from JR East Tohoku Honsen line Shiwa-Chuo station. 20 minutes drive from Tohoku Jidoshado Expressway Shiwa interchange to parking of Shiroyama Park. 

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Pictures (click to enlarge)

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