Ohsawa Castle (Mikawa)
Ôsawajō is a hirayamajiro or okajiro (hilltop castle) ruin with a plain-facing flat section and hilltop redoubt in Mito Township, Toyokawa Municipality. The ôaza (locale) is Toyosawa and the koaza (neighbourhood) is Hikitsuru (not neighbouring Ôsawa). Ruins of Ôsawajō most visibly include a stretch
History
Ôsawajō was the residence of the Hatano Clan in the Nanbokuchō period (14th century), serving as the clan's fortified residence. In 1477, the Hatano defeated the Isshiki Clan, their former masters, in a masterful coup. In 1493, the Hatano were in turn defeated at the battle of Haiźukano by the Makino Clan who took over Ôsawajō. Far from being solely local conflicts, they were influenced by political events developing in the capital. The conflicts in the capital rippled out into the provinces, these waves of turmoil ensaring many castles and clans.
Field Notes
Ôsawajō is a hirayamajiro or okajiro (hilltop castle) ruin with a plain-facing flat section and hilltop redoubt in Mito Township, Toyokawa Municipality. The ôaza (locale) is Toyosawa and the koaza (neighbourhood) is Hikitsuru (not neighbouring Ôsawa). Ruins of Ôsawajō most visibly include a stretch of dorui (earthen ramparts) beneath a small hill. The flat part of the site is now private property, however, and can only be seen from without.
The fort may have extended northward to where the Akiba Shrine is today. The eastern perimeter dorui extends for 70m. The gap in the dorui may indeed be the original entrance to the fort. The almost square outline (the west side being the hill) can be seen on satellite imagery. From the ground, the entrance way shows the shape of the dorui best. A road runs beside here, and perhaps this is where a 50m long dry moat ran which is said to have been once found at the castle.
I checked both the hill behind the enclosed bailey, and the neighbouring ridge to be thorough, but there are no definitive remains there. The hilltop appears partially flattened, and there are terraces beneath it on the opposite side from the lower bailey. These terraces are even lined with stone blocks, but there is nothing to suggest that they weren't piled in later times. "Satoyama (village-mountain boundary zones)" areas like this are full of old terraces and walls, so we mustn't assume they are related to any fortifications.
| Castle Profile | |
|---|---|
| English Name | Ohsawa Castle (Mikawa) |
| Japanese Name | 三河大沢城 |
| Founder | Hatano Clan |
| Year Founded | 14th Century |
| Castle Type | Hilltop |
| Castle Condition | Ruins only |
| Historical Period | Pre Edo Period |
| Artifacts | Dorui |
| Features | |
| Visitor Information | |
| Access | Aichi-Mito Station on the Tōkaidō Main Line; 30 min walk. |
| Hours | Access Limited |
| Time Required | 10 minutes |
| URL | Castle Website |
| Location | Toyokawa, Aichi Prefecture |
| Coordinates | 34.82711, 137.30552 |
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| Admin | |
| Added to Jcastle | 2025 |
| Contributor | ART |
| Admin Year Visited | Viewer Contributed |
| Friends of JCastle | |
| Jōkaku Hōrōki | |
| Umoreta Kojō | |
| Shiseki Yawa | |
| Yogo | |
