Monday, August 24, 2020

Biwajima Castle -Castle of mystic lake and mysterious strategist-

Biwajima Castle

-Castle of mystic lake and mysterious strategist-



Name: Biwajima castle (Biwajima-jo)
Place: Nojiri Shinano-town, Nagano
Type: Island Castle
Built: 14th century?
Remaining remnants: Clay walls and dry moats 

Brief History

Biwajima castle (琵琶島城) spreads over Biwajima island, a mandolin shaped island of about 250 meter long in the north part of Lake Nojiriko. Lake Nojiriko is a second largest one of Nagano prefecture next to Lake Suwako, which is about 3 kilometer long and 2 kilometer wide just the next of border to Niigata prefecture.

Lake Nojiriko is at the middle of two old volcano Kurohime-yama mountain and Madarao-yama mountain, and might be formed by damming up the water by lava of either volcano. Due to high altitude over 600 meter above sea, lake area is used as summer resort in hot reason and snow resort in winter season.

Owing to its cold and still water, Lake Nojiriko preserved terrains of ancient era under the water. Since 1960’s many fossils of Naumann’s elephant, small elephants lived throughout Japan in ice age were found. Furthermore, stone tools of Paleolithic period were also found, then it shows ancient human hunted elephants.

Lake Nojiriko area is a narrow corridor of about 5 kilometer width between Kurohime-yama mountain and Madarao-yama mountain, and east half of corridor is completely occupied by Lake Nojiriko. Therefore it was an important place to control the traffic between Joetsu area of Niigata prefecture and north part of Nagano prefecture, even now used by Joshinetsu Jidoshado expressway, Route 18 and Shinano Tetsudo line.

Origin of Biwajima castle

Biwajima castle was cooperatively used with Nojiri castle at the north shore of Lake Nojiriko. In the beginning of 14th century, the border of Echigo province (Niigata province) and Shinano province (Nagano prefecture) was involved in the conflict between Muromachi Shogunate army at Shinano province and the South Court army at Echigo province.

At this battle Nojiri castle might be used by Muromachi Shogunate army. Later in 15th century Takanashi clan which was the major local lord of Tanakashi clan castle (Nagano prefecture) at current Nakano city expanded their territory toward Iiyama area and Nojiri area. Nojiri castle might be used by Takanashi clan as a border castle toward Echigo province.

Due to the closeness to Echigo province, Takanashi clan had relationship with Nagao clan, the deputy governor of Echigo province. Tamekage Nagao (1486-1543), the leader of Nagao clan and father of Kenshin Uesugi (1530-1578), was born from the daughter of Takanashi clan. When Tamekage Nagao rebelled against the governor Uesugi clan, Takashi clan supported Tamekage and contributed to his victory.

Front line toward Takeda army

But in the middle of 16th century, Shingen Takeda (1521-1578), the warlord of Kai province (Yamanashi prefecture), intruded into Shinano province and expanded this territory. Shingen Takeda ruined Ogasawara clan at Matsumoto basin and Murakami clan at Ueda basin then next aimed Nagano basin where was connected to Uesugi clan.

Kenshin Uesugi who was the governor of Echigo province and fatal rival of Shingen Takeda fought against Takeda army at the battle of Kawanakajima from 1552 to 1564. In 1561 Kenshin gave severe damage to Takeda army at the fourth battle, but Shingen utilized plot in the absence of Kenshin and gradually expanded their territory.

Takanashi clan was suppressed by Takeda clan and had to move to Iiyama castle (Nagano prefecture) at north side of Chikuma-gawa river. Shingen next crossed Chikuma-gawa river westward and built Hekida castle (Nagano prefecture) and Kaesa castle (Nagano prefecture), as a front line toward Echigo province.

Temporal loss and recovery

In 1561, utilizing the absence of Kenshin on the expedition toward Kanto region, Shingen captured Warigatake castle (Nagano prefecture) at the south shore of Lake Nojiriko. Three years later in 1564 Shingen again utilized the absence of Kenshin and attacked Biwajima castle and fell it. 

As Nojiri area was only 30 kilometer apart from Kasugayama castle (Niigata prefecture), the main base of Uesugi clan, Kenshin promptly attacked Biwajima castle and captured. To secure the border, Kenshin newly built Nojiri castle at the north shore of Lake Nojiriko as Biwajima castle in the lake was secure but could not deter the enemy directly.

After the construction of Nojiri castle Uesugi clan prevented the intrusion of Takeda army at this point. After the fall of Takeda clan and incident of Honnoji in 1582, Uesugi clan recovered current Nagano basin, and necessity of defense at Nojiri area decreased then Biwajima castle and Nojiri castle might be abolished around this time.

Structure of Biwajima castle

Biwajima castle has a simple structure of three terraces spreads from the peak of the island toward west. Central area is a rectangular one of about 50 meter long and 30 meter wide, about 20 meter height from water. Central area is divided into upper half which is used as a ground of the hall of shrine, and lower half used for approach.

Ahead of hollows which might be the ruin of dry moat, secondary area of about 50 meter long and 20 meter wide continues westward. Below the step low height terrace surrounds the island at lake water level, which might be used as boat place. Total size of the castle is about 150 meter long and middle size one.

Nojiri castle consists of four terraces separated by dry moats. Central area is 30 meter long square and not so large but had a combined gate at front side. Lower half of the castle is a simple flat areas divided by dry moat, which might be used as camping space. It seems Nojiri castle was a supplementary castle and main castle might be still Biwajima castle.

Tale of strategist of Kenshin Uesugi

In the central area of the castle there is a tomb of Sadayuki Usami, who was told as the strategist of Kenshin Uesugi. According to the military tale “Hokutesu Gundan”, Sadayuki Usami was the founder of Echigo school tactics, and supported Kenshin by his intelligence at the battle against Harukage Nagao (1509-1553) or Shingen Takeda.

Especially at the fourth battle of Kawanakajima in 1561, Sadayuki identified “Kitsutuki (woodpecker) tactics”, a feint operation of Takeda army planned by their strategist Kansuke Yamamoto (?-1561), then contributed to tactical victory of Kenshin. Sadayuki promoted to the vanguard of Uesugi clan and counted as 25 major commanders of Uesugi army.

At last in 1564, Sadayuki played with Masakage Nagao (1526-1564), a distant relative of Kenshin and lord of Sakado castle (Niigata prefecture) who once revolted against Kenshin but became retainer on the ship of Lake Nojiri pond looking moon. Both were drunk then ship upset, then both of Sadayuki and Masakage died from drowning.

Strategist disappeared into water

Masakage Nagao was a talented general and once revolted in the past, and there was a rumor that Masakage attempted rebel again. Sadayuki tried to persuade Masakage to stop the rebel but could not, then to avoid the trouble for Uesugi clan Sadakage sacrificed himself and intentionally sunk the ship with Masakage. Kenshin later praised the loyalty of Sadayuki and built a tomb at Biwajima island.

That is the story about Sadayuki Usami but most part of this tale is thought to be fiction. The model of Sadayuki Usami might be Sadamitsu Usami (1489?-1564), the lord of Biwajima castle at current Kashiwazaki city. Sadayuki Usami actually belonged to Kenshin Uesugi and fought with Masakage Nagao but there was no remarkable achievement.

For the end of Masakage Nagao and Sadayuki Usami, Masakage Nagao is surely recorded to die from drowning, but there is no clear cause for this incident. Besides there is no record of the end of Sadayuki Usami, also his activity at the fourth battle of Kawanakajima.

Background of the tale

Most of the achievement of Sadayuki Usami might be the creation of later generation who insisted to inherit Echigo school tactics. Uesugi clan had many generals but there was no clear military staff compared to Kansuke Yamamoto at Takeda army, then it was necessary to produce the strategist of Kenshin for the purpose of storytelling.

As Sadamitsu Usami was the lord of Biwajima castle at Kashiwazaki city, and Masakage Nagao drawn at Nojiri Pond, Biwajima castle at Lake Nojiriko having same name might be associated to the story of Sadayuki Usami. As stated in 1564 Biwajima castle fell by the attack of Shingen Takeda and there was no possibility to play ship by important generals of Uesugi army.

But apart from the truth, the end of mysterious strategist is suitable for mystic image of Lake Nojiriko. Cool and misty atmosphere of Lake Nojiriko is compared with Nordic area, and the story of genius strategist disappeared in the lake might be close to the legend of King Arthur who gained sword from lade of the lake and departed to Avalon from the lake.

Now no building remains but Biwajima island becomes the ground of Uga Shrine. Formerly a bridge was crossed to the coast but soon lost, then now the island is accessible only by ship and this increases mystic image of Biwajima island. Now Lake Nojiriko is crowded by bass fishing ships. But in the night quiet surface of lake spreads and reminds the tale of mysterious strategist.


15 minutes drive from Joshinetsu Jidoshado Expressway Shinanomachi interchange. Island is accessible by cruise ship or pedal boat.

Related Castles

Pictures (click to enlarge)

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