Thursday, October 8, 2020

Otsuchi Castle -Mountain castle stood physical attacks but succumbed to plot-

Otsuchi Castle

-Mountain castle stood physical attacks but succumbed to plot-


Name: Otsuchi Castle (Otsuchi-jo)
Place: Akahama Otsuchi town, Iwate
Type: Mountain Castle
Built: 14th century?
Remaining remnants: Clay walls and dry moats 

Brief History

Otsuchi castle (大槌城) is located at Shiroyama mountain, one of about 140 meter height from hillside between Otsuchi-gawa river and Kozuchi-gawa river at the center of Otsuchi town. As Otsuchi town spreads along with both rivers, from castle site whole part of town center and Otsuchi bay is clearly seen.

Otsuchi town exists at the middle of Sanriku-Kaigan coast and is about 20 kilometer southward of Miyako city. From Otsuchi area to Ofunato area high mountains exist at just the backside of coast area, then a typical terrain consists of long cape and deep inlet like a comb continues over 30 kilometer. Normally this is a beautiful view of blue sea and green land, but therefore suffered severe damage at the tidal wave of earthquakes.

Origin of Otsuchi clan and Otsuchi castle

Precise year is unknown but Otsuchi castle might be built by local lord Otsuchi clan in 14th century. Otsuchi clan was originally a branch family of Asonuma clan, which was originally a local lord of current Sano city of Tochigi prefecture but later was appointed as the lord of Tono area by Kamakura Shogunate after the fall of Oshu Fujiwara clan.

As Tono area was an inland basin surrounded by Kitakami Kochi mountains, Asonuma clan sent their relative Jiro Tono (?-?) to Otsuchi area at the opposite of mountains to seize marine products at coast area and trade route, in the former half of 14th century. 

Jiro Tono changed surname and became the origin of Otsuchi clan. Among the conflict between Muromachi Shogunate and the South Court at that time, Asonuma clan and Otsuchi clan belonged to different side then became separate clans.

First battle with Nanbu clan

In 1437, Takenami clan who was the local lord of Kesennuma area under Kasai clan attacked Asonuma clan at Tono basin, and Otsuchi clan belonged to Takenami clan in spite of relative of Asonuma clan. Asonuma clan asked assistance to Nanbu clan which grew to strong warlord of the area, then Moriyuki Nanbu (1359-1437), the leader of Nanbu clan, sent reinforcement army.

Reinforcement army of Nanbu clan assaulted the army of Takenami clan and Otsuchi clan the broke it. Pumped up Nanbu army next encircled and Otsuchi clan was forced to the corner. But Otsuchi castle well stood the attack of Nanbu army utilizing sheer cliff and two rivers, then Moriyuki Nanbu died in the battle by a stray arrow and the siege had ended.

After the battle, Otsuchi clan continuously managed Otsuchi area from Otsuchi castle. On the other hand, Asonuma clan which survived the attack of Otsuchi clan also gathered local lords of Tono basin and grew into a major local lord of the area. Otsuchi clan might work with Asonuma clan again, and Otsuchi castle might be expanded as the main base of Otsuchi clan.

Structure of castle

Central area of the castle is an oblong shaped one of about 30 meter diameter, which has a layer of terraces surrounding the top terrace. There remained remnant of pillars then there might be a barrack building at the central area. Westward of central area is separated by saddle area, and ahead of it there were west fort and south fort along with the ridge spreads toward south.

At the east of central area, secondary area, third area and fourth area which are large ones of 100 meter long spreads along with the line of ridge. Currently these areas are simply flat areas but the remnant of barracks, gates or moats were found by excavation. Both sides of these areas are sheer cliff then scenery of hillside is well seen.

About 200 meter ahead of fourth area, at the edge of the ridge, there is Takadate fort which might be a watching place toward south. Total size of core area is about 400 meter, and including surrounding forts it exceeds 700 meter long then it is one of the large castles at Sanriku Kaigan coast area. 

Turbulent situation of Asonuma clan and Otsuchi clan

Asonuma clan prospered at Tono basin over 100 years, but in 1590 it did not visit the military camp of central ruler Hideyoshi Toyotomi (1537-1598) at Odawara campaign and fell into a retainer of Nanbu clan. But Nanbu clan gradually purged local lords in the territory to build centralized authority.

In 1600, during the expedition of Nanbu army to the territory of Mogami clan along with the battle of Sekigahara, Masuzawa clan which was the retainer of Asonuma clan connected with Nanbu clan and seized Tono castle (Iwate prefecture), the main base of Asonuma clan. Hironaga Asonuma (?-?), the leader of Asonuma clan, lost his base then ran to the branch family of Asonuma clan at Kesennma area.

As Asonuma clan at Kesennuma area was a retainer of Masamune Date (1567-1636), who was far stronger than Nanbu clan and aimed Nanbu territory, Hironaga Asonuma was supported by Date army and attacked Tono castle. At this time Otsuchi clan supported Hironaga Asonuma, but Asonuma army could not fall Tono castle and ended its history as the local lord of Tono basin.

Second siege by Nanbu clan and afterward

After the fail of siege of Tono castle, Nanbu army again encircled Otsuchi castle. Hironobu Otsuchi (?-?), the leader of Otsuchi clan, again besieged at Otsuchi castle but could not stand the attack this time and surrendered to Nanbu clan. Under Masasada Otsuchi (?-1616), the successor of Hironobu Otsuchi, Otsuchi clan prospered by marine transportation and development of salted salmon “Aramaki-Sake” which is praised at Edo city. 

But Nanbu clan did not allow the prosperity of Otsuchi clan. In 1616 Nanbu clan purged Masasada Otsuchi for the factless suspect of revolt, then Otsuchi clan ended its history as the local lord of Otsuchi area for 300 years. Nanbu clan kept Otsuchi castle for a while but later built an administrative office at the side of the mountain, then Otsuchi castle was finally abolished in 1659.

Currently no building remains but structure of the castle well remain on the mountain. From castle site the scenery of Otsuchi town under the recovery from severe damage of the earthquake in 2011 is well seen. Same as the past, it is hoped Otsuchi town and Otsuchi castle recover from the damage of incident and prosper as a port town again.


15 minutes drive from Sanriku Jidoshado Expressway Otsuchi interchange to parking of Shiroyama park. 30 minutes walk from parking to hilltop castle.

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Pictures (click to enlarge)

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