Koyama Castle (Kai)

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KaiKoyamajou (44).JPG


Koyamajō was constructed by the Anayama Clan. In 1450 Lord Anayama of Koyamajō sallied forth and attacked Takeda Nobushige at his manor hall in Koisawa, forcing him to commit seppuku. In 1523 Koyamajō was attacked by the Nanbu who had invaded Kai from the south via Torisaka Pass; Lord Anayama Nobunaga fled from the castle and committed suicide. After the fall of the Takeda Clan upon the death of Takeda Katsuyori at the Battle of Tenmokuzan in 1582, Kai Province was carved up between the Tokugawa and the Hōjō clans. Tokugawa Ieyasu appointed Torii Mototada as commander of Koyamajō. Mototada repaired the castle and used it as his base during the Battle of Kurokoma to the east where he defeated Hōjō Ujitada.

Visit Notes

Koyamajō is a well preserved earthworks fortification site on a cliff terrace overlooking the Kōfu Basin. The site features a central fortified compound surrounded by very tall dorui (earthen ramparts) and commensurately deep karabori (dry moats). I found it interesting that even though the fort overlooked steep elevation the builders did not rely on the cliff for defence, but instead took the effort to build ramparts above the cliff line too. This, in my experience, makes Koyamajō more similar to fortifications in the rest of Kantō than in neighbouring Nagano. The dorui and karabori system forms a square shape, and there is a narrow entrance area to the east (a wider section is open to the south but my assumption was that this had been widened in more recent times). In three of four corners of the dorui is some kind of gazebo, and it is easy to imagine that once turrets stood here. The site is maintained as a park but the ramparts and moats are a bit overgrown, and I'm not sure this rural site gets many casual visitors.

Koyamajō had the most impressive fortification ruins of any site I visited on my 'Yamanashi Yashiki Tour' that weekend. The season was in evidence due to the presence of spittlebugs in the grass. In Japanese these spittle-dwelling beetles are called Awafukimushi, reasonably but somehow quaintly translatable as 'bubble-blowing bugs', but called froghoppers in English. I brushed aside some spittle and a fully formed adult beetle with distinctive red portions scurried back into the froth.

  • Main bailey surrounded by tall dorui
  • Dorui (earthen ramparts), Karabori (dry moat)

Castle Profile
English Name Koyama Castle (Kai)
Japanese Name 甲斐小山城
Founder Anayama Clan
Year Founded Before 1450
Castle Type Hilltop
Castle Condition Ruins only
Designations Local Historic Site
Historical Period Pre Edo Period
Artifacts Karabori, Dorui, Kuruwa, Yaguradai
Features trenches
Visitor Information
Access Nearest station is Isawa-Onsen Station on the Chūō Main Line
Visitor Information 24/7 free; park
Time Required 30 minutes
Location Fuefuki, Yamanashi Prefecture
Coordinates 35° 37' 4.55" N, 138° 39' 23.80" E
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Added to Jcastle 2022
Contributor ART
Admin Year Visited Viewer Contributed
Friends of JCastle
Oshiro Tabi Nikki
Jōkaku Hōrōki
Shiro Meguri

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