Japan Castle Explorer: Iwadonoyama Castle -Shameful betrayal or undoubted right-

Iwadonoyama Castle

-Shameful betrayal or undoubted right-

Overview

Name: Iwadonoyama castle (Iwadonoyama-jo)
Alias: Iwadono-jo (Iwadono castle)
Place: Nigiokamachi Otsuki city, Yamanashi
Type: Mountain Castle
Built: 14th century?
Remaining remnants: Clay walls and moats
Title:

Brief History

Iwadonoyama castle (岩殿山城) is built over Iwadonosan mountain, one of about 600 meter above sea level and 200 meter height from hillside, at the north of center of current Otsuki city. Iwadonoyama mountain is an eye-catching mountain of narrow and long body like an end of toothpaste tube, with a naked huge rock wall covers its south slope well seen from Chuo Expressway or Chuo line.

In addition to its shape being protected its whole direction by sheer rock walls and deep valley of Katsura-gawa river, castle site itself is an important point of communication. Otsuki area is a valley of Katsura-gawa river, an upstream of Sagami-gawa river, which flows east and west ward used as a road between Kanto plain and Kofu basin.

From this point, along with tributaries of Katsura-gawa river, northward road runs toward inner part of Okutama area of Tokyo metropolis, and southwestward road spreads to Fuji Yoshida city, a center of north foot of Mt. Fuji and base of climbing. Because of these conditions, Iwadono-san mountain had been an important point at Gunnai area, the eastern part of Kai province (Yamanashi prefecture) from ancient era.

Shugendo temple on mountain

It is said that originally Entsuji temple was built at the place of current Iwadonoyama castle at the end of 9th century. Powerful shape of the mountain was a target of worship, and dangerous rocky roads was used by priests of Shugendo, a mixed religion of mountain faith, to concentrate and free evil thought. At the beginning of 10th century, Entsuji temple had many halls and towers, and temple town developed at hillside.

In 13th century, Entsuji temple prospered as a center of the network of Shugendo mountain temples at Kanto region. At the western edge of Kanto region, along with Chichibu mountains and Tanzawa mountains, holy places of Shugendo mountains such as Mitsumine-yama mountain, Mitake mountain, Takao-san mountain, Oyama mountain toward Mt. Fuji. Iwadono-san mountain places just at the center of this circle, and had many territory around Kai province.

After the fall of Kamakura Shogunate in 1333, Emperor Godaigo (1288-1339) and Takauji Ashikaga (1305-1358) who once cooperated to defeat Kamakura Shogunate, divided and established South Court and Muromachi Shogunate respectively. As Emperor Godaigo was interior at military power but close to Shugendo, South Court kept resistance against dominant Muromachi Shogunate army at mountainous area under the help of Shugendo priest.

Fall of temple and rise of Oyamada clan

At first both power of South Court and Muromachi Shogunate was even at Kai province, but later Takeda clan which was the governor of united and followed to Kamakura Shogunate suppressed South Court supporters and expanded his territory. At this time Entsuji temple lost its role as the center of Shugendo then fell into local temple.

After the fall of South Court supporters in Kai province, Oyamada clan gradually grew their power into local lord. Origin of Oyamada clan is unknown but said as a descendant of Taira clan and was originally a local lord of Chichibu area at current Saitama prefecture. Oyamada clan activated at many battles under Yoritomo Minamoto, the founder of Kamakura Shogunate (1147-1199) then achieved many territories, but was almost ruined being involved in political conflict.

After that the situation of Oyamada clan became unknown for about 200 years, but one family of their descendant might move to Gunnai area including Iwadonoyama castle, one of three large flat areas of Kai province at its eastern edge, and gradually grow their territory. By the end of 14th century, Oyamada clan became a major local retainer of Kai province reigned Gunnai area. Around this time Iwadonoyama castle might be built using former ground of abolished temple.

Subordination to Takeda clan

At Kai province, after the decline of South Court supporters, Takeda clan which was a distinguished family of Minamoto clan since Nobumitsu Minamoto (1045-1127), was appointed as the governor of province. But in 15th century Takeda clan was involved in the revolt of Zenshu Uesugi (?-1417) and once subjugated. Later Muromachi Shogunate restored Takeda clan but their power was weak because of conflict with deputy governor Atobe clan or internal conflicts.

Looking at the disorder of Takeda clan, major local lords of Kai province such as Anayama clan or Oyamada clan tried to become independent lord. But since the end of 15th century, leaders of Takeda clan such as Nobumasa Takeda (1447-1505) or his grandson Nobutora Takeda (1494-1574) proceeded centralization strongly.

Facing pressure from Nobutora Takeda, Oyamada clan once attacked Kofu basin where was the main territory of Takeda clan but was defeated. Furthermore, in 1510, Nobutora Takeda reversely intruded into Gunnai area, and inferior Oyamada clan had to subordinate to Takeda clan. Oyamada clan became a marital relative of Takeda clan and followed but still kept authority for internal administration.

As other local lords of Kai province resisted to Nobutora in cooperation with surrounding warlords, Kai province often suffered from the attack of Imagawa clan which was the warlord of Suruga province (middle part of Shizuoka prefecture) or Hojo clan at Sagami province (Kanagawa prefecture). Especially Sagami province was at the next of Gunnai area thus Oyamada clan was attacked by Hojo army several times. At this time Nobutora reformed Iwadonoyama castle as a border fortress.

Border castle of Takeda clan

In 1541, Harunobu Takeda (1521-1583, later Shingen Takeda), the eldest son of Nobutora, expelled his father to Imagawa clan then became the leader of Takeda clan. Harunobu allied with Hojo clan and Imagawa clan then fixed backward, and started expansion into Shinano province. Nobuari Oyamada (1519-1552) moved his residence to Yamura castle at the center of Tsuru area, and activated as a major general of Takeda clan.

Nobushige Oyamada (1539-1582), son of Nobuari Oyamada, grew up along with the expansion of Takeda clan and activated at many battles of Takeda clan on the invasion to Shinano province or Kozuke province (Gunma prefecture) since young age. In 1568 Shingen broke with Imagawa clan then advanced into Sagami province, and Nobushige served as a vanguard. However, Hojo clan supported Imagawa clan, then Takeda clan and Hojo clan became hostile and Gunnai area became the front of both clan.

In 1569 Shingen Takeda intruded into Hojo territory and siege their main castle Odawara castle, to restrain Hojo army. Beside this Takeda clan might expand Iwadonoyama castle again, then Iwadonoyama castle was praised as three excellent mountain castle of Takeda clan along with Kunozan castle (Shizuoka prefecture) and Iwabitsu castle (Gunma prefecture). It is common for these three castle to be built at mountain with huge rock, and this might be a favor of selection.

Structure of Iwadonoyama castle

Core area of Iwadonoyama castle spreads over a long and narrow ridge of Iwadonoyama mountain which is about 300 meter long and 20 meter width. As the terrain is already a natural fortress protected by cliffs and narrow, only minimum construction is added.

Central area of the castle is a rectangular area of 60 meter long and 20 meter wide at eastern end of ridge, which has a gate area at the western end of area. The eastern edge of the area is the backside of the castle, and protected by a pair of dry moats which is the clearest ruin of the castle.

At the west of central area, several terraces such as secondary area, third area, Nishikuruwa area, Kurayashiki area or Baba area are built along with the ridge. At the below of Kurayashiki area, two ponds are built at small valley to keep rain as water supply. At the west end of the ridge, there is a main gate of hilltop area which is built between two natural huge rocks.

At the small valley at west slope of Iwadonoyama mountain, there are small terraces and dry moat which is said as the main gate of the castle. Ahead of this area, there is a narrow road over huge rock named “Chigootoshi”, which is said as an escape route from castle. This route is a rock climbing route needs to pass holding chains, and has a powerful impression but need close attention to pass it. At the halfway of south wall, there is another flat terrace which might also work as a gate area.

Collapse of Takeda clan

After the death of Shingen Takeda in 1573, his successor Katsuyori Takeda (1546-1582) aggressively fight against central ruler Nobunaga Oda (1534-1582) and his ally Ieyasu Tokugawa (1543-1616). But in 1575, Takeda clan suffered severe defeat at the battle of Nagashino before matchlock gunners of Oda army, and lost many generals and soldiers.

Katsuyori continued desperate fight against Oda clan and Tokugawa clan to keep Takeda clan. But in 1582, with the betrayal of Kiso clan which was the lord of Kiso clan, Nobunaga attacked Takeda clan with overwhelming army from all directions. Katsuyori tried to resist at Suwa province, but because of the loss of Takato castle (Nagano prefecture) and betrayal of Anayama clan, Takeda clan easily collapsed.

Katsuyori who burnt down his residence Shinpu castle (Yamanashi prefecture) visited Gunnai area, to make last resist at Iwadonoyama castle, as recommended by Nobushige. But just at this moment Nobushige forsake Katsuyori and shut the road from Kofu basin to Gunnai area, then Katsuyori who lost his destination place tried to move to Tenmokuzan mountain where was a memorial place for Takeda clan. But being chased by Oda army, Katsuyori and his son Nobukatsu Takeda (1566-1582) died at Tano area where is at the foot of mountain.

Shameful betrayal or undoubted right

After the death of Katsuyori, Nobushige surrendered to Oda army but was executed blaming for his betrayal. Oyamada clan was originally a semi-independent lord under Takeda clan and had a wide autonomy, then for Oyamada clan this was just a change of alliance and their undoubted right. Furthermore, it is said that Oyamada clan tried to avoid involvement of his territory, and was forced to do so by his people.

But for Nobunaga who proceeded centralization and monopoly, it seemed only as a betrayal of hereditary general of Takeda clan. Compared with Anayama clan which leaved Takeda clan in earlier timing and negotiated with Ieyasu Tokugawa, the ally of Nobunaga, it might better for Oyamada clan to plan in advance, but too rapid collapse of Takeda clan did not allow to do so.

After the ruin of Takeda clan, Ieyasu Tokugawa who seized Kai province after the incident of Honnoji in 1582, might use Iwadonoyama castle as a front base against Hojo clan. But after the transfer of Ieyasu to Kanto region in 1590, Asano clan which was appointed by the lord of Kai province under Toyotomi government newly built Katsuyama castle as a base at eastern area, thus Iwadonoyama castle might be abolished at this time.

Afterward of castle

Today all building lost but structure of natural fortress well remains over the ridge of Iwadonosan mountain. Because of the closeness from station, good view and thrilling rock, Iwadonosan mountain becomes a major hiking course for the people of metropolitan area. Panoramic view of Otsuki town from the top of the castle tells a thought of Nobushige Oyamada to protect his territory by any means, even though suffering disgrace of betrayal.

Access

20 minutes walk from JR East Chuosen-sen line Otsuki station to entrance of climbing road. 15 minutes drive from Chuo-Jidoshado Expressway Otsuki interchange to hillside parking. 30 minutes walk from hillside to hilltop castle.