Koujin'o Castle

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AidaKojinojou (1).JPG


Kōjin‘ojō is traditionally said to be a satellite fortification of Takasunejō / Kariyaharajō, but of the two it looks like the more powerful stronghold. Kōjin‘ojō may be another name for Kariyaharajō as referenced in the Kōhakusaiki, a historical document. Takasunejō may also have been this Kariyaharajō. A third option is that Kariyaharajō described a network of castles centred around the area of Kariyahara near the Kariyahara Pass. Sometimes related castles are known collectively by a single, distinct name, so this wouldn’t be so unusual. It may be then that Kōjin‘ojō was actually the main castle in the Kariyahara group, as opposed to what is now called Kariyaharajō (Takasunejō). It’s beyond my powers to speculate, but Ranmaru-sensei hosts an interesting discussion about this mystery on his blog.

For more information see Kariyahara Castle.

Visit Notes

Kōjin‘ojō is a beautiful earthworks castle ruin, emblematic of Shinshū yamajiro (mountaintop castles in Nagano). Local castle fans highly rate it, but it is otherwise unknown, one of Shinano’s well-kept secrets. There is no trail to this site and it sits serene in the wilderness. I approached from a small valley in the east. Features include horkiri (trenches), kuruwa (baileys), dorui (earthen ramparts), and other earthworks.

I really liked the compact, terraced baileys which made up the core the castle. The topmost bailey has remnants of dorui on the western side. The second bailey is below it in the east. There are no paths and one has to climb between the various baileys. There are two spurs from the main bailey, to the north and south. The southern spur is essentially a series of horikiri.

The northern spur is larger and has more horikiri with some narrow enclosures between. The northern spur goes on some way and terminates in a ridge with two horikiri either side, in the northwest and northeast. There is terracing and another horikiri on this northeastern ridge. If one goes down all this way one is rewarded with... climbing all the way back up! The northern portion of the castle is connected to the main, southerly area by a thin ridge which would’ve been perilous to attack along. When I visited there was a beautiful tree with red autumnal leaves here.

I think Kōjin‘ojō would make a good introduction to Nagano’s hidden yamajiro treasures for intermediate castle explorers, but it’s rather difficult to get to the area on public transport, and there are no trails up the mountain. I cycled there from Matsumoto downtown on a mountain road through the Shinagura Pass, and then climbed the eastern ridge directly, using gloves. I thought there may have been some indication of terracing and horikiri remains along this ridge too.

  • Horikiri (trench)
  • Caslte mount from below

Castle Profile
English Name Koujin'o Castle
Japanese Name 荒神尾城
Alternate Names Kariyaharajō
Founder Kariyahara Clan; Ōta Clan
Year Founded Sengoku Period; 1523
Castle Type Mountaintop
Castle Condition Ruins only
Historical Period Pre Edo Period
Artifacts Horikiri, Dorui, Kuruwa, &c
Features trenches
Visitor Information
Access Bus from Matsumoto to Shiga
Visitor Information 24/7; free; mountain
Time Required 60 minutes
Location Matsumoto, Nagano Prefecture
Coordinates 36° 18' 33.80" N, 137° 59' 46.68" E
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Added to Jcastle 2022
Contributor ART
Admin Year Visited Viewer Contributed
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