Ohnuma Castle
Ônumajō is a yamajiro (mounaintop castle) ruin in Ônuma Township, Toyota Municipality. Ruins feature chiefly earthworks such as kuruwa (baileys), horikiri (trenches), dorui (earthen ramparts), dobashi (earthen bridges) and terracing of the mountainside. The castle's structure is mostly linear, compo
History
Ônumajō is said to have been built by Kimura Yasunobu in the late 15th century. The fort may have served as a branch castle of Asuke-Iimoriyamajō. In the Sengoku period, the castellan was Kimura Nobumoto. Ônumajō was attacked and conquered by Takeda Katsuyori's forces in 1574. The Takeda were forced to retreat from Mikawa, however; and, in 1575, Matsudaira Chikakiyo took over as patriarch of the Kimura Clan, rebuilding Ônumajō as a branch fort of Ogyūjō. In 1582, Matsudaira Chikamasa, the new castellan, relocated to Kōzuke on the orders of Tokugawa Ieyasu, and Ônumajō was abandoned.
Field Notes
Ônumajō is a yamajiro (mounaintop castle) ruin in Ônuma Township, Toyota Municipality. Ruins feature chiefly earthworks such as kuruwa (baileys), horikiri (trenches), dorui (earthen ramparts), dobashi (earthen bridges) and terracing of the mountainside. The castle's structure is mostly linear, composed of a chain of baileys ascending as the ridge climbs. It can be split into an upper and lower half, with the top of the lower half being the castle's main bailey.
Terracing of the castle mount becomes apparent nearly as soon as one begins to climb. The third bailey is not far above the valley floor. The third, second and first or main baileys are signposted. There is narrow banding between the third and second baileys and this carved hillside has remained robust in form. The second and third baileys are both terraced.
The main bailey is protected by koshikuruwa (sub-baileys) except to the rear where there is a horikiri. To the west of the main bailey the koshikuruwa is quite wide, and a segment of dorui appears to climb, connecting the ramparts of the main bailey with the terraced bailey below. Some have speculated that this dorui was originally a rising ramp which connected the second bailey to the entrance of the main bailey, compelling invaders to go all the way around beneath the ramparts of the main bailey before ascending to it. However, these days a stairway is situated toward the front of the main bailey so it is not necessary to venture into the sub-bailey. I did anyway so as to see the dorui, of course.
The upper part of the castle is narrower. Beyond a dobashi spanning the horikiri to the rear of the main bailey the ridge climbs. There are two long, terraced baileys between here and the main bailey of the upper castle (which may have been the main bailey of the entire castle though it is not the largest). This upper main bailey is quite small and contains a shrine to a dog god. There is what appears to be dorui behind the shrine. To the rear of the upper main bailey is a trench system and dobashi, as well as indications of tatebori (climbing moats) beneath the ridge. After this the terrain is all natural. A final bailey can be found to the south of the upper main bailey, beneath what looked to me like a former gate site. A path goes back down the mountain here. I didn't follow it, so I don't know if there is more terracing down that way but there may well be.
At the foot of the hill there is a signboard and the start of the trail. To the east is a templed called Tōjuin. I believe this is was originally a funerary temple of one of the ruling clans. To the west there is a flattened 'satoyama' area. It's just fields today but this is where the castle's kyokan (peace-time residential area) used to be.
| Castle Profile | |
|---|---|
| English Name | Ohnuma Castle |
| Japanese Name | 大沼城 |
| Founder | Kimura Yasunobu; Kimura Nobumoto |
| Year Founded | Late 15th Century; Sengoku Period |
| Castle Type | Mountaintop |
| Castle Condition | Ruins only |
| Historical Period | Pre Edo Period |
| Artifacts | Dobashi, Dorui, Horikiri, &c. |
| Features | trenches |
| Visitor Information | |
| Access | Along National Route 301, turn at Shimoyama Family Mart; hiking trail is opposite Tōjuin temple |
| Hours | 24/7 free; mountain |
| Time Required | 60 mins |
| Location | Toyota, Aichi Prefecture |
| Coordinates | 35.04403, 137.32109 |
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| Admin | |
| Added to Jcastle | 2025 |
| Contributor | ART |
| Admin Year Visited | Viewer Contributed |
| Friends of JCastle | |
| Jōkaku Hōrōki | |
| Umoreta Kojō | |
| Oshiro Tabi Nikki | |
| Yogo | |
