Koshimizu Castle
This was once a large and important castle that played a pivotal role in the history of the region, a castle through which many great personages passed and major events turned. Unfortunately, nothing remains of this storied site today. A single stone marker beside an elementary school and a barely l
History
Koshimizu Castle was first built around 1516 by Kawarabayashi Masayori, a powerful retainer of Hosokawa Takakuni. The castle stood on a low plateau north of Nishinomiya, overlooking the route between Kyoto and the port of Hyogo-tsu. It featured moats, earthen ramparts, and multiple baileys.
In 1519, the Ryō-Hosokawa War erupted when Hosokawa Sumimoto and Miyoshi Yukinaga rose against Takakuni. The rebels captured Koshimizu Castle, but Yukinaga was soon defeated and killed at the Battle of Tōji-in (1520), allowing the Kawarabayashi to recover their stronghold. The castle changed hands again in 1527, when Hosokawa Harumoto and Miyoshi Motonaga marched on Kyoto, and later in 1533, when Kawarabayashi supporters allied with the Ikko-shū briefly retook it before being expelled by Miyoshi.
By the late 1530s, Koshimizu had become the strategic Settsu base of the Miyoshi clan, linking their homeland in Awa with the Kinai region. Miyoshi Nagayoshi, son of Motonaga, established his residence there in 1539 and successfully repelled an assault by Itami Chikatsugu in 1541. From this point, Koshimizu functioned as the headquarters of the Miyoshi Nagayoshi as he expanded his influence across the Kinai region.
In 1549, Nagayoshi convened a decisive council of war at Koshimizu after discovering that Miyoshi Masanaga had caused his father’s death. When Hosokawa Harumoto refused to surrender Masanaga, Nagayoshi turned against him, launching the Battle of Eguchi, the conflict that marked his independence from the Hosokawa.
When Nagayoshi moved into Akutagawasan Castle, Matsunaga Hisahide was appointed castellan of Koshimizu Castle with authority over the surrounding district and the Koshimizu-shū (越水衆), local kokujin loyal to the Miyoshi.
In 1566, amid internal struggles between Hisahide and the Miyoshi Triumvirate (三好三人衆) fell to Shinohara Nagafusa. Later that year, Ashikaga Yoshihide, supported by the Miyoshi faction, entered Koshimizu Castle and was recognized by the court as shogun.
When Oda Nobunaga entered Kyoto in 1568, Shinohara abandoned the site and retreated to Awa. Ashikaga Yoshiaki temporarily occupied the castle before moving back to Kyoto as the 15th shogun. In 1570, Shinohara returned with 20,000 men from Awa and Sanuki, again capturing Koshimizu, but a peace settlement with Nobunaga soon followed. The castle was abolished under Nobunaga, ending the complex history of this site.
Field Notes
This was once a large and important castle that played a pivotal role in the history of the region, a castle through which many great personages passed and major events turned. Unfortunately, nothing remains of this storied site today. A single stone marker beside an elementary school and a barely legible history panel are now passed daily by schoolchildren and dog walkers. A second small monument lies buried in weeds, tucked between a new home and an abandoned lot.
I visited Koshimizu Castle for its connection to Miyoshi Nagayoshi, the first tenkabito, and Matsunaga Hisahide, first Lord of Yamato, as part of my exploration of this under appreciated period in Japanese history — the years before the rise of Nobunaga.
| Castle Profile | |
|---|---|
| English Name | Koshimizu Castle |
| Japanese Name | 越水城 |
| Alternate Names | 小清水城, 腰水城 |
| Founder | Kawarabayashi Masayori |
| Year Founded | 1516 |
| Castle Type | Hilltop |
| Castle Condition | Ruins only |
| Historical Period | Pre Edo Period |
| Features | |
| Visitor Information | |
| Access | Shukugawa Station (Hanshin Kobe Line), 15 min walk; Nishinomiya Station (JR), 10 min bus, 5 min walk |
| Hours | School grounds, be considerate |
| Time Required | 5 mins |
| Location | Nishinomiya, Hyogo Prefecture |
| Coordinates | 34.74565, 135.33681 |
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| Admin | |
| Added to Jcastle | 2025 |
| Contributor | Eric |
| Admin Year Visited | 2025 |
| Admin Visits | October 11, 2025 |
| Friends of JCastle | |
| Jokaku Horoki | |
| Shirobito | |
| Kojodan | |
