Kai Koyama Castle
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.
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.
|English Name||Kai Koyama Castle|
|Year Founded||Before 1450|
|Castle Condition||Ruins only|
|Designations||Local Historic Site|
|Historical Period||Pre Edo Period|
|Artifacts||Karabori, Dorui, Kuruwa, Yaguradai|
|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|
|Added to Jcastle||2022|
|Admin Year Visited||Viewer Contributed|
|Friends of JCastle|
|Oshiro Tabi Nikki|