Oshi Castle

Timeline

1. Around 1478

   Narita Founding

   Narita Masakuni and his son Akiyasu overthrow the Oshi clan, vassals of the Ogigayatsu Uesugi, and build a fortress on the marshlands of Gyoda.

2. 1479

   Peace with Uesugi

   Uesugi forces attack the new castle but a settlement is brokered by chief minister Ota Dokan, leaving Narita rule intact.

3. 1574

   Uesugi Kenshin's Siege

   Uesugi Kenshin besieges the castle on a Kanto campaign and burns its town, but the marshland fortress refuses to fall.

4. 1590

   Siege of Oshi (Water Attack)

   Ishida Mitsunari's 23,000 men attempt the famous water siege; the castle does not sink and surrenders only after Odawara falls, earning the 'Floating Castle' nickname.

5. 1590

   Matsudaira Tadayoshi Installed

   After Tokugawa Ieyasu's transfer to the Kanto, his fourth son Matsudaira Tadayoshi takes the castle as seat of the 100,000-koku Oshi Domain.

6. 1639

   Abe Tadaaki's Expansion

   Senior counselor Abe Tadaaki enters Oshi and begins the major Edo-era expansion that adds the three-story tower and a new layout.

7. 1702

   Layout Completed

   By the Genroku 15th year the Abe complete the final castle layout and town planning of Oshi as a mature early-modern fortress and post town.

8. 1871

   Han Abolition, Oshi Prefecture

   With the Meiji abolition of feudal domains the prefectural office of newly created Oshi Prefecture briefly occupies the second bailey before merging into Saitama.

9. 1873

   Decommissioning

   Oshi Castle is decommissioned and most structures dismantled, leaving only part of the main bailey embankment.

10. 1988

    Museum and Tower Reconstruction

    The Gyoda City Local History Museum opens on the main bailey site, with the three-story tower rebuilt in reinforced concrete as its centerpiece.

11. 2012

    Film 'Nobou no Shiro' Released

    Wada Ryo's novel is adapted for cinema, dramatizing the 1590 water siege and giving Oshi Castle nationwide name recognition.

12. 2017

    Continuation 100 Castles and Heritage

    Selected as Continuation 100 Famous Japanese Castles number 118 and added as a component of the Japan Heritage 'Tabi Warehouses of Gyoda' story.

Detailed History

Oshi Castle was completed around 1479 by Narita Akiyasu, who with his father Masakuni had overthrown the Oshi family, vassals of the Ogigayatsu Uesugi, and raised a fortress on marshland between the Tone and Ara rivers. The following year the Uesugi attacked, but chief minister Ota Dokan brokered peace and the Narita kept the area. Allegiances shifted as the Hojo grew dominant in the Kanto. In 1559 Uesugi Kenshin arrived from Echigo and the Narita briefly submitted; in 1561 lord Narita Nagayasu joined Kenshin's siege of Odawara, but defected after Kenshin's inauguration as Kanto Kanrei. In 1574 Kenshin himself besieged Oshi and burned its town, yet the marshland fortress would not fall. The legendary battle came in 1590, when Hideyoshi began his Kanto pacification. Lord Narita Ujinaga had moved to Odawara to fight under the Hojo banner, leaving uncle Suesue with about 619 samurai and 2,000 local conscripts. The Toyotomi force numbered 23,000 under Ishida Mitsunari, with Otani Yoshitsugu, Natsuka Masaie, and Sanada Masayuki at his side. Mitsunari set his HQ atop Maruhakayama Kofun and built a 28-kilometer dike — the Ishida Levee — to flood the castle from the Tone River. The castle refused to sink, and only when Odawara itself surrendered did the defenders capitulate, giving Oshi its lasting nickname, the 'Floating Castle'. After Tokugawa Ieyasu's transfer to the Kanto, his fourth son Matsudaira Tadayoshi took the castle, which became the seat of the 100,000-koku Oshi Domain. In 1639 senior counselor Abe Tadaaki entered and began a major expansion that produced the three-story tower and the final layout completed by 1702. The Abe were transferred to Shirakawa in 1823, and Matsudaira Tadataka of the Okudaira-Matsudaira line came from Kuwana. The Meiji abolition of feudal domains in 1871 briefly installed Oshi Prefecture's office in the second bailey, but the castle was decommissioned in 1873 and most structures dismantled. The site became Narita Park, then Oshi Park, and in 1949 a city baseball ground occupied the main bailey. After the ground relocated, the Gyoda City Local History Museum opened there on 17 February 1988, with the three-story tower rebuilt in reinforced concrete as its centerpiece. In 2017 Oshi joined the Continuation 100 Famous Japanese Castles as number 118, and on 28 April became part of Japan Heritage 'The City of Tabi Warehouses — Gyoda'.

Cultural Significance

Oshi Castle is counted among the seven famous strongholds of the Kanto and is the only Hojo-allied castle to have withstood Hideyoshi's force to the end. The names 'Floating Castle' (Uki-jo) and 'Turtle Castle' (Kame-jo) derive from its wetland setting and its legendary refusal to sink. Through the Edo period the castle was the seat of fudai and shinpan daimyo, and under four generations of the Abe family the castle town flourished as a back-route stage of the Nakasendo and a Tone River logistics hub. From the late Edo era Gyoda established itself as a center of tabi-sock production, an industry that continued into modern times and led to the 2017 Japan Heritage inscription of 'The City of Tabi Warehouses — Gyoda', of which the castle is a component. Wada Ryo's bestselling novel Nobou no Shiro and its 2012 film adaptation starring Nomura Mansai dramatized the water siege and brought Oshi to a national audience far beyond Sengoku enthusiasts. The castle ruins are a Saitama Prefectural Historic Site, with earthworks of the main bailey embankment still in place. The Kitaya-mon gate was relocated to Soganji temple in Kazo, and the gate of the domain school Shinshukan stands south of the museum. Every November the Oshi Castle Period Festival, on the second Sunday, recreates the era with a samurai procession and matchlock firing in the castle moat.

Architectural Details

Oshi was a flat castle that exploited its marshland setting to the fullest. The local terrain was originally a vast swamp dotted with islands of dry ground formed by natural levees, and the castle's builders left the swamp in place — turning each island into a bailey linked to the next by bridges. The earliest layout dispensed with a keep entirely, leaving the main bailey as open ground while the lord lived in the second bailey, producing a fortress that was 'hard to attack and easy to defend'. The Edo-period senior counselor Abe Tadaaki carried out the great expansion, organizing the main, second, third, and Suwa baileys into a coherent layout girded by water moats, and built the three-story tower as the castle's symbol. Equivalent to a keep, the original tower rose three stories with white shikkui lime plaster walls contrasting against the dark board cladding of its base — a hallmark of the Edo-castle aesthetic. The current tower, rebuilt in 1988, is a reinforced-concrete exterior reconstruction set in a different position and scale from the historic original, though its design follows the 'Oshi-jo bird's-eye view' and other sources. The castle town's defenses ingeniously used the surrounding swamp and waterways in place of conventional moats, and the original marshland survives in part as Suijo Park to the south.