Senmi Castle


Senmijou (1).jpg


Senmijō was first built by the Obinata Clan, vassals of the Murakami Clan, to protect the mountain passes which led to their territory from the west. On the otherside of the mountains was the territory of the Nishina Clan. This was during the first half of the 16th century.

In 1552, Takeda forces invaded Azumi County, and Yamagata Masakage attacked Senmijō. The fierce battle saw castellan Obinata Nagatatsu slain, and the castle fall under Takeda control. In subsequent years the castle changed hands due to in-fighting within the Obinata Clan. The clan was split between supporting the Takeda and resisting, and this dispute became an all out civil war within the clan (see Fumimichi Castle). But in 1555 the pro-Takeda faction of the Obinata took back the castle from the rebels.

Many defeated clans in Nagano, like the Murakami Clan, fled to Echigo to be with Uesugi Kenshin following the advance of Takeda Shingen. However, the Kai-Takeda Clan met its final demise in 1582 (see Taira-yashiki), and thereafter Uesugi Kagekatsu took back territory in Shinano, including Senmijō which became a frontline castle against the resurgent Ogasawara Clan (former official governors of Shinano Province).

Ogasawara Sadayoshi ordered the Nishina Army to attack Senmijō in 1584, and they successfully conquered the castle, only to see it fall back into Uesugi Kagekatsu's hands a couple of months later. The Nishina attacked once more that year, but this time failed to capture the mountain fortress. The following year, 1585, Ogasawara Sadayoshi successfully conquered Senmijō, and that year installed Futatsugi Morimasa as castellan, who rebuilt the castle.

In 1590, following the fall of Odawara to Toyotomi Hideyoshi which cemented his position as undisputed leader of Japan, Uesugi Kagekatsu, defying the general trend toward peace that Toyotomi-kampku (regent) was trying to encourage, brazenly attacked Ogasawara lands, and re-captured Senmijō in the autumn. The kampaku was not best pleased, and ordered Uesugi Kagekatsu to retreat, which he did. Thereafter Ishikawa Iemasa was appointed castellan of Senmijō.

Visit Notes

Senmijō is a yamajiro (mountaintop castle) ruin in the north of Miasa Township, Ômachi Municipality. Senmijō, deep within the mountainous interior of Shinano, is a barely visited and underexplored site. Indeed, I was able to make a tremendous discovery at this ruin, namely a large trench complex which has gone unidentified by Yogo-sensei and Ranmaru-sensei, the castle-bloggers whose maps I was using to navigate the site. The spirit of adventure and thrill of discovery is very much alive in this quiet place.

Senmijō features horikiri (trenches), dorui (earthen ramparts), tatebori (climing moats), kuruwa (baileys) and other earthwork ruins. Ranmaru divides the castle complex into three fortresses: an upper A-Fort, a lower B-Fort, and a detached C-Fort. Indeed, the site is quite expansive.

Whilst searching for the route to the C-Fort annex, I noticed a tatebori climbing the mountainside beside the trail. I climbed up this chute (keeping pace with a lizard scurrying at my feet), and discovered a large horikiri located between the A and C forts. This trench is not depicted on any maps of the castle I have seen, and so I'm happy to claim it as my own discovery.

"ART's Trench (please indulge me)" is not some ambiguous divot, but a very well formed and preserved trench complex, with an impressive depth of about 2 m on the descending side, and some 5m on the rising side of the ridge. It is situated on an otherwise unworked ridge section with no baileys attached, which is curious. The structure is of a central trench segment with a steep climbing section to the south, and a careening section to the north where it joins up with a creek. This creek seems to have been augmented as a defensive line to stop lateral movement on the mountainside, and there is a 'U'-shaped egress at the bottom of this chute. If I had stumbled into this falling section I would've no doubt been catapulted off the mountain like an awry pinball.

There is an embankment overlooking the trench on the descending side. It has some gnarly old trees and clumps of grass, and to me was a small oasis from whence I admired the beauty of the sculpted earth. Below the embankment I could only see the tops of trees. Later, retracing my steps after climbing up the scarp to A-Fort, I realised that the path I was on when I noticed the tatebori section of the trench is the path descending to the C-Fort from B-Fort, and that beneath the trench and berm is a cliff of sheer, smooth rock. This was confounding. Why did the castle-builders dig a deep trench along a ridge which was impossible to reach from below?

I'm not one for making up my own theories, amateur as I am, but I got to thinking how C-Fort was accessed originally from the rest of the castle. It was likely from C-Fort that the rest of the castle was accessed, but was as it by that tiny path which now exists going from B-Fort, or were there large ascending bridges, perhaps hikibashi (draw-bridges), connecting C-Fort with A-Fort over cliff and trench? If the enemy breached C-Fort and the bridges were withdrawn or collapsed, it would be extremely difficult for them to then enter the rest of the castle. This is just my outlandish idea, but how else can we account for this large trench here?

In my excitement about the highlight of visiting this site for myself, I forgot to talk about the layout of the site. A-Fort is the main bailey complex, and it is protected on the ridge-side rear by a large dorui segment or bulwark carved from the mountain itself. In fact, it seems that the main bailey's terraces were made by simply digging away at the mountain, but leaving the rear portion as a barrier of earth. The ridge leading up to the main bailey complex has horikiri and dorui. In A-Fort there is a lower, secondary bailey. Dorui is evident on the left side when descending.

Descending a sloped section from A-Fort one comes to B-Fort. It has a bailey section with some residual dorui, but the most interesting thing about this part of the castle is the row of three horikiri between boulders. The foremost of these horikiri is very large. Actually, it was a nuisance to get down into safely, and took me some time (I didn't even go back up that way, but opted to try to take the mountain slope to C-Fort). At the very end of the castle proper, on the tip of the ridge, are many boulders, and two large standing stones in the rough shape of diamonds stand like guardsmen either side of the ridge. They seemed purposeful, and this impressed me. I wondered if these monoliths had been set up that way intentionally for the fortress.

Finally, C-Fort is on a smaller ridge away from A and B up top. I visited it on my way back down the mountain. There are some horikiri, kuruwa and a dorui segment, but nothing too interesting in comparison to the other ruins (excepting "my" trench between it and the main fortress, of course!). It is thought this area was used to store supplies, and that the entrance to the main fortress originally came through here.

  • "ART's Trench"
  • Horikiri (trench) discovery, seen from above
  • Another trench to the rear of the site
  • Boulder sentinels

Castle Profile
English Name Senmi Castle
Japanese Name 千見城
Founder Obinata Clan
Year Founded Early 16th Century
Castle Type Mountaintop
Castle Condition Ruins only
Historical Period Pre Edo Period
Artifacts Dorui, Horikiri, Kuruwa, &c.
Features trenches
Visitor Information
Access Shinano-Ômachi Station on the Ôito Line; rental e-bike
Visitor Information 24/7 free; mountain
Time Required 150 minutes
Location Ômachi, Nagano Prefecture
Coordinates 36° 36' 26.46" N, 137° 54' 58.64" E
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Added to Jcastle 2023
Contributor ART
Admin Year Visited Viewer Contributed
Friends of JCastle
Kojō Seisuiki

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