Sunday, July 26, 2020

Imai Castle -Cliff edge castle of Uesugi clan at border-

Imai Castle

-Cliff edge castle of Uesugi clan at border-



Name: Imai castle (Imai-jo)
Place: Kamigo-Oidaira Tsunan town, Niigata
Type: Mountain Castle
Built: 16th century
Remaining remnants: Clay walls and moats 

Brief History

Imai castle (今井城) is located at the edge of Oi-daira, a huge river terrace of 100 meter height from river water formed by Shinano-gawa river at the west of Tsunancho-town. Castle site is only 3 kilometer apart from the border of former Shinano province and Echigo province, currently Nagano prefecture and Niigata prefecture.

Shinano-gawa river, which is the longest one in Japan, flows northward from Nagano basin to Iiyama area then curved to eastward then passes the narrow valley between Sekida Mountains and Mikuni mountains toward Tokamachi basin. Even though a narrow valley, this is a route from Nagano basin toward Chuetsu area of Niigata prefecture then currently used as Iiyama-sen line or Route 117.

The border of Nagano prefecture and Niigata prefecture longs over 50 kilometer east and westward, between Hakuba mountain and Nozawa mountain both are famous ski resort. The main route across the border is Myoko Kogen route at westward, which is a gentle and wide area used by Joshinetsu Jidoshado Road and Route 18. Another route is a Shinano-gawa valley route at eastward, where Imai castle exists.

Origin of Imai castle

The origin of Imai castle is not clear but it might be built around the middle of 16th century. Castle site is a huge terrace of about 5 kilometer long and 2 kilometer wide encircled by Shinano-gawa river at north, Shikumi-gawa river at west and Nakatsu-gawa river at east, separated into three parts by creek valley.

Akazawa terrace, which is the largest one occupies east half, was the center of the area and had a village at the center of the terrace. This terrace also had Akazawa castle, an older and small castle just separated the north edge of the terrace by dry moat. Akazawa castle faces downstream of the river toward Tsumaari castle, which was the local center of the area at the center of current Tokamachi city.

In the middle of 16th century, the tension at the border of Shinano province and Echigo province risen along with the conflict of Shingen Takeda (1521-1573), the warlord of Kai province (Yamanashi prefecture), and Kenshin Uesugi (1530-1578), the one of Echigo province (Niigata prefecture).

Tension at border

After five time battle of Kawanakajima between both armies, Shingen Takeda seized whole part of Nagano basin and further approached the border. Uesugi army firmly kept Iiyama castle (Nagano prefecture) and north side of Shinano-gawa river, bearing the attack of Takeda army.

But at the south side of the river, Ichikawa clan which was the local lord of Kijima-daira village longed to Takeda army, being famous for the latter of Shingen passed from Kansuke Yamamoto (?-1561), a legendary military staff of Shingen. Now the power of Takeda army reached to the border at Shinano-gawa valley, and it was a possibility of the attack of Takeda army to this area to shut the support to Iiyama castle or obstruct the excursion of Uesugi army to Kanto region.

To strengthen the border, Uesugi clan newly built Imai castle closer place to the border. From the castle the border of the province is directly seen, and also a climbing road from river side to Akazawa terrace is looked down. Compared with Akazawa castle, it was a better place to watch the border and guard Akazawa village.

Structure of Imai castle

Imai castle stands over a peninsular like terrace between two creeks at the north edge of the terrace. Northward, eastward and westward of the castle is encircled by sheer cliff, and only south ward of the castle is connected to backside of the terrace. Common to this type cliff edge castle, the castle had concentric circle shaped moats from the edge  to create areas.

Central area is a triangle shaped one of about 40 meter long, which is separated by thick and tall clay wall and 15 meter wide and 15 meter depth dry moat separated into compartment from secondary area, East side slope of the area is protected by combination of vertical dry moats frequently seen at Uesugi clan castles, and north side slope is protected by attached terraces and dry moats.

Secondary area is a rectangular one of about 80 meter long and 40 meter wide, which is separated into upper terrace and lower terraces. Southward of the area is separated by deep dry moat and clay wall, which is folded at the side of main gate to make side attack to main gate. 

Outside of the main gate there is a small square shaped buffer area, which might be connected to main gate by bridge across outer dry moat. Total size of the castle is about 200 meter long and 100 meter wide then not so large, but firmly built defense structures shows the importance to protect this border from Takeda army.

Internal conflict of Uesugi clan

In 1578, at the internal conflict of Uesugi clan between Kagekatsu Uesugi (1556-1623) and Kagetora Uesugi (1554-1579) after the death of Kenshin Uesugi, Katsuyori Takeda (1546-1582), the successor of Shingen Takeda, at first supported Kagetora Uesugi under the ally with Hojo clan, the warlord of Sagami province (Kanagawa prefecture) and origin of Kagetora Uesugi.

Katsuyori Takeda marched to the border of Shinano province and Echigo province then suppressed Kagekatsu Uesugi, both for Myoko Kogen area toward Kasugayama castle (Niigata prefecture) where Kagekatsu resides, and for Shinano-gawa valley toward Tokamachi basin and Muikamachi basin were the origin of Kagekatsu Uesugi.

However, Kagekatsu Uesugi forced to the corner by Takeda army negotiated with Katsuyori Takeda to his side. If Kagetora Uesugi won the battle under the support of Hojo clan, the power of Hojo clan adding Uesugi territory will far exceed Takeda clan then Katsuyori already damaged at the battle of Nagashino would subordinate to Hojo clan soon.

Turn of Katsuyori Takeda

Further, Kagekatsu Uesugi offered the large amount of fund and cession of territory such as Itoigawa area or Kozuke province (Gunma prefecture) to Katsuyori. This was an attractive condition to Katsuyori who struggled the restoration of the army and authority after the fatal defeat at the battle of Nagashino.

Finally Katsuyori Takeda turned to the supporter of Kagekatsu Uesugi. Katsuyori once coordinated between Kagekatsu Uesugi and Kagetora Uesugi, but because of the attack of Tokugawa clan Katsuyori had to cease from Echigo province, and utilizing this opportunity Kagekatsu Uesugi could reversely suppress Kagetora Uesugi and finally ruined it.

Among this negotiation between Kagekatsu Uesugi and Katsuyori Takeda, the border of Shinano-gawa-river area was not ceded to Takeda clan because it might be included the territory of Ueda Nagao clan, the origin of Kagekatsu Uesugi. Komorizawa clan and Kaneko clan, the general of Imai castle, firmly protected the castle against Takeda clan till the coordination of Katsuyori Takeda and Kagekatsu Uesugi.

Afterward of castle

In 1582, Katsuyori Takeda was ruined by the attack of central ruler Nobunaga Oda (1534-1582), who already broke Takeda army at the battle of Nagashino in 1575. At the same time Kagekatsu Uesugi was also forced to the corner by Oda army, but just at this point Nobunaga Oda died in the incident of Honnoji, a coup d’etat by his general Mitsuhide Akechi (1521-1582).

As Oda army which lost their lord retreated from former Takeda territory, barely survived Kagekatsu Uesugi captured Nagano basin after confrontation with Hojo clan. Border of Uesugi clan moved forward, and it became not necessary to protect the border at Shinano-gawa river area then Imai castle might be abolished around this time.

Now all building was lost but structure of the castle such as clay wall and dry moat perfectly remains on the cliff. Usually due to weathering clay walls and dry moats become lower and shallow even though remaining, but Imai castle keeps roughly original height and depth, even though not clear from the result of renovation or not.

From castle deep valley of Shinano-gawa river is looked down under cliff. Structure of the castle and stream of the river shows the connection and conflict of Takeda clan and Uesugi clan at this quiet border area, interacted each other and finally result in the fall of Takeda clan and survival of Uesugi clan.


45 minutes drive from Kanetsu-do Expressway Ishizawa-Shiouti interchange to parking space in front of the castle via Route 363 ad Route 117. Trace the sign from Route 117 to parking space.

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Pictures (click to enlarge)

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