The original site of Kaiźujō, known now as Zenkaiźujō to distinguish it from the later castle which would become Matsushirojō, was built by the Takeda in 1559. According to the Kōyō Gunkan, it was the enigmatic Takeda general Yamamoto Kansuke who oversaw the castle's construction. Construction was carried out by Kōsaka and Yashiro clansmen. Yamamoto appointed Oyamada Toramitsu as garrison commander, with Ichikawa Hitonaga and Hara Yosōzaemon as sub-commanders. Zenkaiźujō was built to prosecute Takeda Shingen's infamous conflict with Uesugi Kenshin, and played an integral role in the Kawanakashima campaigns. In 1561 Kasuga Toritsuna, who had taken over command, withstood a siege at the castle by Uesugi forces whilst he awaited reinforcements from the main Takeda army. In 1582, after the fall of the Takeda, Mori Nagayoshi took over command of Kaiźujō, making it his residence. It wasn't long, however, before Mori's lord, Oda Nobunaga, perished at Honnōji, and this prompted Mori to flee Shinano for Mino. He had gathered various Takeda family hostages to live at the castle, and he used these as a shield to cover his retreat from Shinano. Uesugi forces thereafter took over the castle, filling the power vacuum left in the wake of recent events, and held it throughout their conflict with the Ogasawara and up until their move to Aiźu in 1598. Tamaru Naomasa was appointed by Toyotomi Hideyoshi as castellan thereafter, by which time the castle was mostly used as a storage depot. In the Edo period Zenkaiźujō was suceeded by Matsushirojō which originally shared its name. Zenkaiźujō was itself originally built over the site of a fortified residence of the Kiyono Clan who had fortified the nearby mountaintops.
Zenkaiźujō is now the site of the temple district of the jōkamachi (castle town) of Matsushirojō. I believe this is the original site of Kaiźujō, the castle which became Matsushirojō. It is therefore properly called Kaiźujō, but since many people call Matsushirojō "Kaiźujō" it is also called "Former Kaiźujō" to distinguish it from Matsushirojō. Funny, I thought, nobody ever calls Matsumotojō "Fukashijō" anymore! The site of Zenkaiźujō overlaps with the outer extremities of Matsushirojō where the town was subsequently built up. I was intrigued to find a long hillock hiding beneath funerary architecture in one of the temple's cemeteries. Could this random elevation be the remains of dorui (earthen ramparts) of the original castle? Dorui are indeed said to remain, and this was the only place that I could detect them. Otherwise the area has been re-developed since the Edo period as the centre of Matsushiro Domain.
|English Name||Zenkaizu Castle|
|Alternate Names||Kaiźujō 海津城|
|Castle Condition||Ruins only|
|Historical Period||Pre Edo Period|
|Access||No. 30 bus from Nagano Station to Matsushiro Station (35 mins); 10 minute walk|
|Visitor Information||24/7; Free; Temple|
|Time Required||20 minutes|
|Location||Nagano, Nagano Prefecture|
|Coordinates||36° 33' 38.45" N, 138° 12' 11.38" E|
|Added to Jcastle||2021|
|Admin Year Visited||Viewer Contributed|