Saturday, November 2, 2019

Oguni Castle (Dewa, Shonai) -Castle to protect distant new territory-

Oguni Castle (Dewa, Shonai)

-Castle to protect distant new territory-


Name: Oguni castle (Oguni-jo)
Place: Oguni Tsuruoka city, Yamagata
Type: Mountain Castle
Built: 14th century?
Remaining remnants: Clay walls and moats 

Brief History

Oguni castle (小国城, different from another Oguni castle of Dewa province at Mogami providence) is built over Shiroyama mountain, one of about 250 meter height from hillside just behind of Oguni village in the south part of current Tsuruoka city. Oguni village is a small one at the valley of Shonai Oguni-gawa river, and exist five kilometer apart from the border of current Yamagata prefecture and Niigata prefecture.

Murakami city which is at the north edge of Echigo plain and Tsuruoka city of Shonai plain is separated by 60 kilometer long hilly area of Asahi mountains. But even though in such distant mountainous area long roads were built to connect two plain from ancient era to now.

Now Route 7 which runs along seashore in the north part and inland in the south part, and Route 345 traces opposite side connects both area, but both roads merge and run along the coast at the border of two prefectures. But in the past, there was a direct route which connected inland part of these two roads and passed the border across passes.

Two roads connect Shonai plain and Niigata plain

This road was called as Dewa Kaido road, and was originally built in 8th century to connect Iwafune castle at Murakami area and Dewa castle at Sakata area built by ancient Yamato government. Dewa Kaido road had two routes, one is coast road which passed Nezugaseki gate, and inland road across Horikiri Toge pass.

Today because of huge engineering work broad and flat road is built at coast side, but in the past this coast road was dangerous and unstable road runs rippling cliffs. Contrary to this, inland roads was winding and necessary to cross hills but relatively safe and could use villages on the way as posting place. Due to this, main route was inland road at medieval era.

This inland road runs north and south ward across the valley of rivers flows westward, and the valley of Shonai Oguni-gawa river had the largest flat area and population thus worked as border town at the side of Dewa province (Yamagata prefecture). Also this place is at the middle of the border area and suitable to control whole border line.

Origin of Oguni castle

Precise year is unknown but Oguni castle was originally built as the main base of local lord Oguni clan. At that time there was a record of Oguni Hyogonokami who was the leader of Oguni clan belonged to the South Court and fought against Daihoji clan supported Muromachi Shogunate, and Oguni castle might be built in such conflict.

Under the decline of the South Court, Oguni clan also followed to Daihoji clan and became its retainer. Daihoji clan itself subordinated to Uesugi clan, the governor of Echigo province (Niigata prefecture), at the opposite of the border from Oguni area. Due to this situation there was no tension at the border thus Oguni castle at this point might be a small one.

In the middle of 16th century, Daihoji clan became its short term perk period under Yoshiuji Daihoji (1551-1583) who was the lord of Oura castle (Yamagata prefecture), under the support from Kenshin Uesugi (1530-1578), the strong warlord of Echigo province. But Daihoji clan lost the support of Uesugi clan due to the internal conflict of Uesugi clan after the death of Kenshin.

Seizure of new territory and need for defense

Upset Yoshiuji Daihoji tried to establish his authority by aggressive military operation but failed thus was assassinated by his retainer Tozenji clan. Tozenji clan was supported by Yoshiaki Mogami (1546-1614) who just united Yamagata basin and tried to proceed to Shonai plain. Tozenji clan and Mogami army broke remaining Daihoji clan in 1585, thus Shonai plain once became new territory of Mogami clan.

However, at the opposite of the border, there was Shigenaga Honjo (1540-1614) who was the brave retainer of Uesugi clan and lord of Murakami castle (Niigata prefecture). Honjo clan had close relationship with Daihoji clan as a coordinator between Uesugi clan and Daihoji clan.

As Daihoji clan which lost Yoshiuji Daihoji adopted the son of Shigenaga as its leader at last stage, Shigenaga waited for the chance to recover Shonai area from Mogami clan. It took time to march from Yamagata basin to Shonai plain passing narrow and long valley of Mogami-gawa river or tough mountainous route of "Rokujuri-goe", Oguni castle might be significantly strengthened by Mogami clan preparing for the intrusion of Honjo clan.

Structure of Oguni castle

Central area of the castle is a rectangular one of 50 meter long and 30 meter wide, wholly surrounded by clay wall. At the east of central area, there is a gap of clay wall which is the main gate of the area. At the east of central area secondary area and third area which are same size of central area but just a flat terrace are built on the slope.

Entrance of third area is protected by small clay wall at the front to prevent direct entrance of the enemy. At the east of third area, below sheer slope, there is a large and narrow flat terrace of 80 meter long named Komatateba, which is an entrance of climbing road from hillside and meeting place of soldiers.

At the west of central area ahead of deep dry moat, there is a large flat space of 100 meter long and 50 meter wide which consists of many small frat terraces. This area is called as "Nishi Ooyashiki" (west large residence) and might be used as hilltop residence of the commander, camping space or storage space. Total size of the castle is about 500 meter long and one of the largest mountain castles of the province.

Loss of Shonai plain

In 1588, utilizing the absence of Yoshiaki Mogami who had to face with Masamune Date (1567-1636) to support Osaki clan at Pacific Ocean side, Honjo clan sent large army to recover Shonai plan. The defense line of Mogami clan including Oguni castle was broken, and Honjo army broke Tozenji clan at the battle of Jugorigahara and captured Shonai area.

After that Honjo clan lost the territory at Shonai area being blame for the raise of local residents, and Shonai plain became the territory of their master Uesugi clan. But in 1598, Uesugi clan was moved from Echigo province to Aizu area of Mutsu province (Fukushima prefecture) retaining Shonai area as before.

Echigo province was managed by Hori clan then Shonai area becomes a detached territory of Uesugi clan, and Oguni castle faces with external power again. West part of the castle has the atmosphere of the castles of Uesugi clan and might be added at this time.

Recovery of Shonai area

In 1600, correlating the conflict of Ieyasu Tokugawa (1543-1616) and Mitsunari Ishida (1560-1600) after the death of central ruler Hideyoshi Toyotomi (1537-1598), Kagekatsu Uesugi (1556-1623) raised his army and attacked Yoshiaki Mogami. From Shonai area Uesugi army departed toward Yamagata basin and captured Shiraiwa castle at northwest part of the basin.

But Mogami army well resisted at Hasedo castle (Yamagata prefecture), and in the meantime Ieyasu Tokugawa broke Mitsunari Ishida at the battle of Sekigahara. Uesugi clan allied with Mitsunari and was expected as next target, Uesugi army retreated from Mogami territory to protect their territory.

Mogami army marched to vacant Shonai area and achieved their earnest wish to hold fertile Shonai plain. Yoshiaki lived at Tsurugaoka castle (Yamagata prefecture) as his retirement place to watch his new territory, and Oguni castle firmly worked as border castle. But after the death of Yoshiaki, in 1622 Mogami clan lost their territory due to their internal conflict.

Afterward of castle

Oguni castle might be abolished by Ikkoku Ichijo Rei (one domain one castle rule) in 1615. But Sakai clan which became the lord of Shonai domain after the leave of Mogami clan also recognized the importance of Oguni area and placed border gate at the hillside. Oguni town prospered by the end of Edo era as a posting town of Dewa Kaido road.

Now all building was lost but structure of the castle well remain over the mountain. Even though not having stone walls, but well built flat terraces and defense facilities shows the tension for the seizure of Shonai plain and strong will to protect it by holders. Contrary to secure castle, castle town at hillside preserves the atmosphere of peaceful posting town having traditional houses at both side of the road. 


15 minutes drive from Nihonkai Tohoku Jidoshado Expressway Atsumi-Onsen interchange.

Related Castles

Oguni Castle (Dewa, Mogami) -Castle protected small basin of snow and spa-
Oura Castle -Castle of too aggressive lord who lost its backer-
Murakami Castle -Northern fortress-
Tsurugaoka Castle -Peaceful castle of domain of good governance-

Pictures (click to enlarge)

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