Japan Castle Explorer: July 2020

Yamanaka Castle (Mikawa)

-Long journey to Pax Tokugawana (4) appearance of young hero-

Overview

Name: Yamanaka castle (Yamanaka-jo)
Alias: Iouzan-jo (Iouzan castle)
Place: Maiki-cho Okazaki city, Aichi
Type: Mountain Castle
Built: Around 1500
Remaining remnants: Clay walls and dry moats
Title:

Brief History

Continued from Part 3

Yamanaka castle (山中城） is located over Shiroyama mountain, one of about 120 meter height from hillside at the south east of Meiden-Yamanaka station and Route 1. Castel site is at the edge of Mikawa Kogen height, a line of hills spreads from northeast to southwest toward Mikawa-wan bay which separates Okazaki plain and Toyohashi plain.

Route 1, Tomei Expressway and Meitetsu line passes Mikawa-Kogen height through a valley of Goyu fault, and Yamanaka castle exists at the western end of this narrow corridor. Shiroyama mountain is roughly a part of Mikawa-Kogen height, but it is an independent hill surrounded by two creeks and separated from backside mountains.

Origin of Yamanaka castle

Precise year is unknown but Yamanaka castle might be built by local lord Saigo clan around 1500. Saigo clan was originally a deputy governor of Mikawa province (east half of Aichi prefecture) under the governor Nitsuki clan, and originally held a territory around Okusa castle (Aichi prefecture) at the north part of current Kota town.

In the latter half of 15th century, Saigo clan ascended northward across Oto-kawa river, and built Okazaki castle as the bridgehead toward north. But this movement resulted in the conflict with Matsudaira clan, which seized Iwatsu castle (Aichi prefecture) and attempted to expand southward to Okazaki plain.

Suppressed Saigo clan finally accepted Mitsushige Matsudaira (?-1508), the fifth son of Nobumitsu Matsudaira (1404-1488), the third leader of Matsudaira clan, as his successor. Saigo clan turned to Okazaki Matsudaira clan, and built Yamanaka castle at the east end of their triangle territory at the east of Yahagi-gawa river.

Rise of Anjo Matsudaira clan

It is said that Yamanaka castle is built for the fort in case of emergency, but considering the size and location it might be used as a main base of the clan. Okazaki castle at that time and Okusa castle were small castles on singular area, and not suitable for besiege. Furthermore, Yamanaka castle was a suitable place considering possible expansion toward Toyohashi plain.

However in 1506, Imagawa clan which was the lord of Suruga province (middle part of Shizuoka prefecture) intruded into Mikawa province under the order of Sozui Ise (1456-1519, famous as Soun Hojo) who was a guest general of Imagawa clan at that time. Okazaki Matsudaira clan suffered severe damage and might lost its leader, thus relative of Saigo clan succeeded it and returned its surname to Saito clan.

On the other hand, Anjo Matsudaira clan at the opposite of Yahagi-gawa river resided at Anjo castle (Aichi prefecture), well stood the attack of Sozui Ise under its leader Nagachika Matsudaira (1473-1544), the fifth leader of Matsudaira clan. Anjo Matsudaira clan merged Iwatsu Matsudaira clan, the original main family of Matsudaira clan but also suffered severe damage from Imagawa army, and became the leader of Matsudaira clan.

Appearance of young hero and capture of Yamanaka castle

But this change of main family brought severe discord to families of Matsudaira clan. The leader of Matsudaira clan was handed to Nobutada Matsudaira (?-1531), but Nobutada could not cope with this situation then other families of Matsudaira clan did not follow to Nobutada and there might be a possibility of revolt.

Looking at this situation, preparing for the invasion of Imagawa clan, in 1523 families of Matsudaira clan discussed and decided the retirement of Nobutada Matsudaira and succession to Kiyoyasu Matsudaira (1511-1535), the eldest son of Nobutada Matsudaira but only 13 years old at this time. Here came a young hero as the leader of Matsudaira clan.

Kiyoyasu Matsudaira showed the braveness in the youth and other families of Matsudaira clan gathered under him, but Saigo clan left the group of Matsudaira family showed the attitude of independence and deprived the territory of Matsudaira clan. Therefore Kiyoyasu Matsudaira decided to attack Saito clan, to protect his authority.

In 1526, under the plot of his retainer Okubo clan, Kiyoyasu Matsudaira attacked Yamanaka castle which was a branch castle of Okazaki castle at that time. By capturing Yamanaka castle, Main base Okazaki castle was separated from the south half of the territory of Okazaki clan, and also support from Toyohashi basin across Mikawa-Kogen height.

Being forced to the corner, Nobusada Saigo (?-1525), the leader of Saigo clan, surrendered to Kiyoyasu Matsudaira and let his daughter marry with Kiyoyasu. Kiyoyasu decided Okazaki castle as his main base then totally reformed Okazaki castle into large castle and established castle town. Similarly, Yamanaka castle might be improved as east gate of the territory and expecting future expansion toward east.

Structure of Yamanaka castle

Yamanaka castle is built over the ridge spreads east and westward over 400 meter. At the peak of the mountain, central area that is about 30 meter long and 15 meter width, and secondary area which is about 50 meter long and 20 meter wide is built at almost same height. Secondary area is wholly surrounded by clay wall, which is the character of castle built or reformed by Imagawa clan.

At the east of core areas, there is a 20 meter long square shaped eastern area which is a key area for the defense toward east. Below this eastern area terraces are built over two ridges spread northward and east ward. Each line of terraces have dry moats at choke point and folded road to obstacle approach of enemies which area advanced technologies.

Contrary to this, westward of core areas are protected by simple layer of three corridor areas. Considering sheer slope this part is older structure with less facilities, and might keep original style of the castle. Originally this castle might be built by Saigo clan toward west, and later Matsudaira clan, Imagawa clan or Tokugawa clan expanded castle structure toward east.

Total size of the castle is about 400 meter long and 200 meter wide, and one of largest mountain castles of Mikawa province along with Nagasawa castle opposite of Mikawa Kogen height.. Finally this castle are expected as the last defense line of Okazaki area toward east, especially at the time of Shingen Takeda (1521-1573), the warlord of Kai province (Yamanashi prefecture) to Mikawa province around 1570.

Sudden decline of Matsudaira clan

Kiyoyasu Matsudaira who seized Okazaki area in 1526 aggressively attacked surrounding lords and united west half of Mikawa province by 1529. Next Kiyoyasu Matsudaira marched to the east of the province and united whole part of Mikawa province at that year, only six years from the succession of Matsudaira clan and still 19 years old.

But Kiyoyasu Matsudaira died in accident of Moriyama castle (Aichi prefecture) in 1535, and Matsudaira clan fell into severe trouble such as external pressure from Oda clan of Owari province (west half of Aichi prefecture) or Imagawa clan, and internal conflicts of relatives.

Matsudaira clan which lost Anjo area by invasion of Oda clan asked assistance to Yoshimoto Imagawa (1521-1560), and Imagawa army occupied Mikawa province. Imagawa clan thought important of Yamanaka castle as a road between Okazaki castle and their own territory, thus Imagawa army reformed Yamanaka castle and stayed.

Afterward of castle

After the battle of Okehazama in 1560, Ieyasu Tokugawa (1543-1616), the grandson of Kiyoyasu Matsudaira, left Imagawa clan and became an independent lord. Ieyasu entered Okazaki castle soon captured Yamanaka castle from Imagawa army, preparing for the attack by Imagawa army from eastward.

After that Yamanaka castle was not involved into battle, and might be kept as local military base by Tokugawa clan. In 1590, after Odawara campaign of central ruler Hideyoshi Toyotomi (1537-1598) against Hojo clan, Ieyasu Tokugawa was moved to former territory of Hojo clan in Kanto region. At this time Yamanaka castle might be abolished.

Today no building exists but structure of the castle well remain on the mountain. From watching place at the north slope of the mountain Route 1 or Meitetsu line is well seen, and it clearly shows this castle stands aside Tokaido Road, the main artery of the nation. Technically built structures not seen in most part of mountain castle in the province shows continuous importance of this castle for each holders.

Continue to Part 5

Access

30 minutes walk from Meitetsu Nagoya-Honsen Meiden-Yamanaka station. 20 minutes drive from Tomei Expressway Otowa-Gamagori interchange to visitor's parking lot in front of Haguri hospital. 20 minutes walk from entrance of climbing road to hilltop castle.