Japan Castle Explorer: Oguni Castle (Dewa, Mogami) -Castle protected small basin of snow and spa-

Oguni Castle (Dewa, Mogami)

-Castle protected small basin of snow and spa-

Overview

Name: Oguni castle (Oguni-jo)
Alias:
Place: Honjo Mogami town, Yamagata
Type: Mountain Castle
Built: 1581?
Remaining remnants: Clay walls and moats
Title:

Brief History

Oguni castle (小国城, different from another Oguni castle of Dewa province at Shonai area) is built over Ohirama mountain, one of about 100 meter height from hillside at the east of the center of current Mogami town. Mogami town exist at the northeastern corner of current Yamagata prefecture, and covers whole part of Oguni basin, the small one of about 5 kilometer square at the border to Miyagi prefecture and known for having several spas.

Oguni basin is an important communication road toward Pacific Ocean side from Shinjo basin to Pacific ocean side, because the height of Oshu mountain which separates Tohoku region is quite low at this basin then it was a gentle slope where the railway could pass without passing tunnel. On the other hand, as snowy area blow from the Sea of Japan gathers at this basin because of terrain, this basin is heavy snow area.

Local lords of Shinjo basin

At the beginning of 16th century, current Shinjo basin and Oguni basin were separately held by many small lords but later three roads grew to the leader of each area. Sakenobe clan which was the lord of Sakenobe castle had the north half of Shinjo basin, and Shimizu clan which held Shimizu castle kept south half of the basin.

On the other hand, Oguni basin which was separated from Shinjo basin by mountains and rivers became the territory of Hosokawa clan. Hosokawa clan was a tributary and highest class retainer of Muromachi Shogunate at Kyoto city, but might have their territory at Oguni basin and send their relative.

Hosokawa clan gradually grew to the holder of Oguni basin, then built Iwabe castle at the place of Oguni castle, where is the center of the basin and meeting point of Oguni-gawa river and Kinude-gawa river as their main base, In addition to this, Hosokawa clan also built Shimode castle as their branch castle at Shimo area, where was the entrance of the basin from westward.

Advance of Mogami clan toward north

In the middle of 16th century, Mogami clan which was the lord of Yamagata castle and governor of Dewa province (Yamagata prefecture) significantly declined because of internal conflicts and confrontation against Date clan, a strong warlord of Yonezawa basin. Major local lords of Yamagata basin gathered at Tendo clan which was the lord of Tendo castle, and Hosokawa clan belonged to this ally.

However, Yoshiaki Mogami (1544-1614), the new leader of Mogami clan who won the internal conflict against his father, raised his army to restore the authority of Mogami clan. But just at the north of Yamagata area which was the territory of Mogami clan, Tendo clan stayed at secure Tendo castle and prevented the expansion of Yoshiaki.

At first Yoshiaki Mogami directly attacked Tendo castle but failed, then tried to weaken the power of Tendo clan by tempting or ruining other local lords supported Tendo clan from backside. After capturing Kaminoyama castle (Yamagata prefecture) and securing his backside, Yoshiaki his campaign toward north part of Yamagata basin in 1581.

Fall of Hosokawa clan

As Hosokawa clan hostile to Yoshiaki in the past conflict against his father, Yoshiaki sent large army to Oguni basin across Nadagiri toge pass. Hosokawa clan tried to intercept Mogami army and both armies crushed at Mankigahara at the south of Oguni castle, but outnumbered Hosokawa clan lost this battle then Hosokawa clan disappeared from history.

After the battle, Yoshiaki placed his retainer Mitsumoto Oguni (?-?) as the lord of Oguni basin. Mitsumoto newly built Oguni castle at the place of former Iwabe castle then governed the basin. Utilizing Oguni castle, Yoshiaki advanced into Shinjo basin then soon held Shinjo basin by ruining Shimizu clan and turning Sakenobe clan.

After the separation of Tendo clan and their supporters, Yoshiaki Mogami could ruin Tendo clan in 1584 and united Yamagata basin. After the unification of Yamagata basin, Yoshiaki continued struggle against surrounding lords and expanded his territory. Oguni castle became an important branch castle of Mogami clan preparing for Onodera clan at northward and Date clan at eastward.

Structure of Oguni castle

Oguni castle spreads over the slightly curved ridge of Ohirayama mountain. Central area of the castle is a rectangular one of 100 meter long and 50 meter wide, having a large backside clay wall at its northern line. At the backside of central area, there is a buffer area which is separated by huge clay wall over 20 meter wide and 20 meter depth from backside mountain.

In front of central area, several terraces are built like a step to the halfway of mountain. Approach route toward hilltop is run at the side of these terraces, and enemy soldier might be exposed to the upward attack from these terraces. On the other hand, gate into hilltop area is not so sophisticated compared with castles of later period such as Nobesawa castle.

At the hillside there are many flat spaces might be used as ground for the residence of retainers. Outer barrier surrounded the mountain toward the next ridge, and the valley between two ridges might be used as a residence of the lord. Total length of the castle exceeds 500 meter, and is regarded as one of the major branch castles of Mogami clan.

Afterward of castle

Finally after the battle of Sekigahara occurred in 1600, Yoshiaki became the lord of whole Dewa province and recovered past fame of Mogami clan. But after the death of Yoshiaki, Mogami clan was expelled by Edo Shogunate by severe internal conflict in 1622. At this time Oguni castle was confiscated by Sendai domain and was destructed, and Oguni clan was sent to Saga domain.

After the loss of the castle, Oguni town prospered as a route of transferring commodities which was shipped from the main shipping route at the Sea of Japan and went up Mogami-gawa river then landed at Shinjo basin to Sendai area. Basho Matsuo (1644-1694), a famous Japanese poet, passed Oguni basin during his long round journey of Tohoku region.

Today no building was left but structure of the castle well remain on the mountain. Layers of small terraces at hillside well show the feature of castle built by Mogami clan. As the castle site apart from the center of the town, castle site still keep the atmosphere of old castle town along with scattered outer barrier, temple and shines surrounding the mountain in the snowy basin.