Aoyagi Castle -Stone built castle at the border of two basins

Aoyagi Castle

-Stone built castle at the border of two basins

Overview

Name: Aoyagi castle (Aoyagi-jo)
Alias:
Place: Sakakita Chikuhoku village, Nagano
Type: Mountain Castle
Built: 14th century?
Remaining remnants: Stone walls, clay walls and moats
Title:

Brief History

Aoyagi castle (青柳城) is located at the peak of Shiroyama mountain, one of about 200 meter height from hillside and the western end of the ridge spreads from Azumaya-yama mountain. Castle site faces meeting point of Omi-gawa river and Tojo-gawa river which are tributary of Sai-kawa river, and also at the middle of narrow valley of 5 meter long formed by two rivers.

Matsumoto basin and Nagano basin, both are major basin of Shinano province (Nagano prefecture), are separated by the line of Chikuma mountains. Although Sai-kawa river which forms Matsumoto basin runs across the mountains toward Nagano basin, but this is over 20 meter long narrow valley and not suitable for large size transportation.

Instead of this, although it was necessary to over Sarugababa pass and Yagose pass, mountainous road runs through the valley of Omi-gawa river and Tojo-gawa river was developed as more stable and closer route. Even now, highway, railway and Route 403 similarly run through this narrow valley connecting Matsumoto basin and Nagano basin.

Origin of Aoyagi castle

Precise year is unknown but Aoyagi castle was built by local lord Aoyagi clan. Aoyagi clan was a branch family of Omi clan which held Omi area just at the north of Aoyagi castle, and descendant of Ogasawara clan. Ogasawara clan was a branch family of Takeda clan which was a major family of Minamoto clan and later became the warlord of Kai province (Yamanashi prefecture).

Ogasawara clan made achievement for Muromachi Shogunate and was appointed as the governor of Shinano province in the middle part of Muromachi era. But being limited by geography of the province separated into small basins, Ogasawara clan could only manage south half of the province including Matsumoto basin and Ina valley.

Contrary to this, north part of the province was independently held by large local lords such as Murakami clan, Takahashi clan or Nishina clan. Especially Murakami clan which was based at Katsurao castle (Nagano prefecture) just ahead of Sarugababa-pass was equivalent to Ogasawara clan for both of power and authority.

Front line castle toward Nagano basin

In the latter half of 15th century, Ogasawara clan was separated into three families and conflicted each other then significantly lost their power. Contrary to this, Murakami clan already surpassed its internal conflict gradually grew their power and expanded toward east. There was no clear record of conflict between Ogasawara clan and Murakami clan, but Aoyagi castle might work as border castle of Ogasawara clan toward Murakami clan.

However, in the middle of 16th century, Shingen Takeda (1521-1573) who was the warlord of Kai province started expansion toward Shinano province. Shingen first captured Suwa providence the attacked Murakami clan but was defeated at the battle of Uedagahara by Yoshikiyo Murakami (1501-1573).

Looking at the defeat of Shingen, Nagatoki Ogasawara (1514-1583), leader of Ogasawara clan, attacked Takeda army but failed at the battle of Shiojiri-Toge in 1548. Reversely Shingen intruded into Matsumoto basin, and in 1550 Shingen captured Hayashi castle (Nagano prefecture), the main base of Ogasawara clan. Ogasawara clan lost their territory and left the province.

Capture and usage by Takeda clan

At this time Aoyagi clan followed to Shingen and became his retainer. Next Shingen attacked Murakami clan and encircled its major branch castle Toishi castle, but suffered defeat before Murakami army again. However, in 1551, Shingen captured Toishi castle by the plot, and two years later Murakami clan left Katsurao castle.

By defeating Murakami clan Shingen entered into Nagano basin, but this was also a start of 10 year battle against Kenshin Uesugi (1530-1578), the warlord of Echigo province (Niigata prefecture) and was praised as the “god of the war”.

As Shingen mainly sent supplies from Fukashi castle (later Matsumoto castle) at Matsumoto basin to the front at Nagano basin, Aoyagi castle became an important castle to protect supply line. Aoyagi castle was reformed by Takeda army and might be managed by Nobufusa Baba (?-1575), an important general of Takeda clan held Makinoshima castle (Nagano prefecture) and Fukashi castle. It was recorded that Shingen actually stayed at this castle.

Structure of Aoyagi castle

Aoyagi castle is built over straight line ridge of the mountain spreads toward east and west. Central area of the castle is a rectangular one of 50 meter long and 20 meter wide, at the western end of the ridge. Large size clay wall which might be used as the basement of the building at both end of the area, and about 3 meter tall stone wall was built at northern line of the area where is well seen from the hillside road.

At the east of central area, five small terraces are built over the ridge. The terrace of east end might be a main entrance of the castle, which has small masugata style composite gate and is protected by stone wall. South slope of the ridge is relatively gentle thus several layer of corridor are built to prevent climbing of enemies.

Ahead of vertical deep dry moat, another group of terraces are built at eastward, Areas in this part is not so shaped and might keep original style built by Aoyagi clan. But east end of this area also has another vertical huge dry moat which merges to eastern one at the middle of the slope, which might be integrally added by Takeda clan. Total size of the castle is about 350 meter long, and its size and structure shows the importance of the castle.

Transition of situation

After struggles Takeda clan pushed out Uesugi clan from the south part of Nagano basin, then the situation of Aoyagi castle tentatively stabilized. But after the fall of Takeda clan in 1582 and collapse of central ruler Oda clan which ruined Takeda clan at that year, Aoyagi castle became the front between two basins again.

Looking at the collapse of Oda clan, Uesugi clan barely survived before the attack of Oda clan reversely captured Nagano basin. Next Uesugi clan sent the refugee of Ogasawara clan to Matsumoto basin and once captured Fukashi castle held by Kiso clan.

However, another refugee of Ogasawara clan supported by Ieyasu Tokugawa (1543-1616), the former ally of Oda clan and warlord of Pacific Ocean coast, entered into Matsumoto basin and deprived Fukashi castle. Now Ogasawara clan at Matsumoto basin and Uesugi clan at Nagano basin faced at this place.

Afterward of castle

As both of Uesugi army and Tokugawa army had another important front, there were only small conflicts at this front. But from 1582 to 1583, there were four time change of the lord of Aoyagi castle between Uesugi army and Ogasawara army. During this conflict Aoyagi clan disappeared, and Ogasawara clan finally held this castle placed their retainer Matsubayashi clan as the commander.

Ogasawara clan kept Aoyagi castle as branch castle by 1590, but after the Odawara campaign of central ruler Hideyoshi Toyotomi (1537-1598) their territory were confiscated then Ogasawara clan turned to the retainer of Ieyasu Tokugawa. Ishikawa clan which became next lord of Matsumoto basin might abolish Aoyagi castle.

Now no building was left but structure of the castle well remain on the mountain. Stone wall of central area is well kept but it is difficult to see the whole shape as it is built on sheer slope and difficult to enter inside. Scenery of the valley including multiple roads shows the importance of the valley which connects two basins and importance of the castle to control it.

Access

60 minutes walk from JR East Shinonoi-sen line Sakakita station. 30 minutes drive from Nagano Jidoshado Expressway Omi interchange to the parking backside of the castle.