Ohtsubono Fort

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KaiOhtsuboRui (16).JPG


Ôtsubo-rui, despite ample ruins remaining, is a mysterious fortification site. The clan who first built and inhabited this medieval fortified residence and redoubt is not known, but it is conjectured that the Yamaki Clan, an off-shoot of the Tsugane Clan and members of the Tsuganeshū, a border force under the Takeda of Kai, called this fort their home. In that case the builder was probably Yamaki Kazusanosuke.

Ôtsubo-rui measured about 200m on each side, and was divided into at least three baileys and multiple enclosures by earthworks such as moats and earth-piled ramparts. These various fortifications actually made the fort quite cramped despite its overall fairly large footprint, and so it is speculated that the lord’s residence was located either in a tertiary bailey or outside of the fortified space itself. Most of the defences were orientated west, and this is where the elevation is greatest; to the north and east the cliff recedes and connects to a plateau. The residence may have been located below with the fortified clifftop used as a redoubt then.

There is also the theory that Ôtsubo-rui was built as an encampment during the Tenshō Jingo rebellion. Since the Hōjō held the smaller fort to the south, Ôtsubo-toride, did they also construct Ôtsubo-rui? Given the scale of the site, larger and more intricate than a typical residence, this may well be the case. It’s also possible that Ôtsubo-rui was indeed originally the residence of some lord, perhaps Yamaki Kazusnosuke, but that it was re-purposed and expanded by Hōjō forces during their stand-off with Tokugawa Ieyasu.

Visit Notes

Ôtsubo-rui is a fortified residence site in the Minowa area of Takane Township in Hokuto Municipality, Yamanashi Prefecture. At first I found no way into this forested site, and initially gave up to visit other sites in the area. Finding remains at similar looking sites in the vicinity, I determined it was worth having another crack at this one, so I began by encircling the site. There is a beautifully preserved old residence in the west, with a thatched roof cottage and gatehouse. I chose to enter the field behind here. I did not expect to find much. However…

I found that the wooded area was situated on high ground. The elevation looked sculpted in a linear fashion rather than wholly natural, and I scrambled up the scarp. Sure enough, atop of the embankment the earth had been mounded into a parapet. This was dorui (earthen ramparts) then. I continued into the forest, which was really a cedar plantation, and found that it was overgrown with bamboo grass. Proceeding with little vision I came to a long depression. Snow had gathered here. I realised this was a karabori (dry moat), and that I had penetrated the inner fort, and got quite excited.

I took a closer look at satellite images and saw that there was an angular gap in the trees here. The snow had fallen through and gathered in the moat. I could photograph and follow the moat this way. Although it didn’t get particularly easier to photograph, I found that the moat got deeper to the east, and there was dorui on the inside of the karabori. The karabori is preserved on three sides: west, north and east. To the south the hill slopes off and there is housing, so it appears the moat may have been filled in or cut away there, but due to overgrowth I couldn’t confirm either way. I contented myself with going around three sides of the inner bailey, sometimes pausing to fight back bamboo grass, until I found a trail rudely cut through the overgrowth to the east which led out of the forest.

I was very happy with my discovery here. Since the blogger I was following, the gentleman castle blogger who runs the blog O’shiro Tabi Nikki (‘Castle Travel Diaries’), had apparently been defeated by the site, I had little to go on, and didn’t know what to expect (Yogo-sensei also called it quits (but to be fair to him he did try in summer), but the guy at Kojōshi did a cracking job; I’ll link all blogs below). To find such extensive remains of earthworks was a big discovery for me. The site was overgrown and wet, but luckily I was wearing some new water-proof gear, so I was able to push through the bush fearlessly, exploring the central area, though many ruins remained hidden by flora. Mission (mostly) accomplished then.

Ôtsubo-rui is not to be confused with Ôtsubo-toride to the south, which I visited on the same day. Both ‘rui’ and ‘toride’ can be translated as ‘fort’ in English, ‘rui’ referring to earthworks; although, I will say, it seems that ‘rui’, at least in Kai and Suruga, mostly refers to a residence of some sort. Places referred to as ‘rui’ also often take the possessive particle (as in 大坪の塁), so in English I will also refer to this site as ‘Ohtsubono Fort’, and the later constructed and smaller Ôtsubo-toride to the south as ‘Ohtsubo Fort’. Considering both sites are in the same place, there’s little other way to distinguish without using Japanese vocabulary.

  • Dorui
  • Karabori / dry moat earthworks
  • Dorui

Castle Profile
English Name Ohtsubono Fort
Japanese Name 大坪塁
Alternate Names Ôtsubo-rui
Founder Yamaki Kazusanosuke or Hōjō Ujinao
Year Founded Sengoku Period
Castle Type Hilltop
Castle Condition Ruins only
Historical Period Pre Edo Period
Artifacts Dorui, Karabori
Features trenches
Visitor Information
Access Sudama IC
Visitor Information 24/7 free; forest
Time Required 60 minutes
Location Hokuto, Yamanashi Prefecture
Coordinates 35° 49' 23.12" N, 138° 25' 24.02" E
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Added to Jcastle 2023
Contributor ART
Admin Year Visited Viewer Contributed
Friends of JCastle
Oshiro Tabi Nikki

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