忍城
Oshi Castle
Overview
Oshi Castle in Gyōda, Saitama, is Japan's most celebrated 'water castle' — a fortress built on marshy islands amid the interlocking waterways of the Oshi, Motoare, and Hoshi rivers. Founded by the Narita clan around 1478, it achieved immortal fame by surviving a massive flood-siege engineered by Ishida Mitsunari in 1590: Mitsunari constructed a 28-kilometer earthwork dam to inundate the castle, but a garrison of just 500 defenders held out for over three months — refusing to fall even as Odawara Castle surrendered. The heroic defense, led in legend by the warrior-woman Kaihime (daughter of the castle lord), was dramatized in the 2012 film 'Nobou no Shiro' (The Great Castle of Water), bringing nationwide fame. The current three-story replica tenshu (1988) houses the Gyōda City Folk Museum. The area also holds Japan's largest cluster of ancient burial mounds, making Gyōda a city of extraordinary historical depth.
Connection to Swords
Oshi Castle's sword connections center on the fierce close-quarters fighting of the 1590 water siege. Mitsunari's flood strategy was designed to avoid direct assault — but when defenders broke out to raid the earthwork dams, brutal wetland combat followed, where short blades (tantō and wakizashi) suited for tight, unstable footing were essential. The legendary Kaihime, who reportedly wielded a spear in the castle's defense, exemplifies the samurai warrior-woman tradition in which sword, spear, and naginata training was integrated. The Narita clan samurai carried practical 'Musashi swords' — blades forged by Kantō smiths valued for toughness over aesthetic refinement. Gyōda City Museum (inside the replica tenshu) displays Narita and Abe clan armor and sword fittings, alongside ancient iron swords from the nearby Sakitama burial mounds — offering a rare span of blade history from the 5th century to the Edo period in a single visit.
Highlights
- Replica tenshu and Gyōda City Museum — displays Narita and Abe clan armor and swords; the real history behind 'Nobou no Shiro'
- Ishida Embankment ruins — remnants of Mitsunari's 28-kilometer flood dam, a monument to audacious military engineering
- Kaihime historic trail — castle-town walk tracing the legend of Oshi's warrior heroine
- Sakitama Ancient Burial Mounds — a nationally designated Special Historic Site with Japan's largest concentration of 5th–7th century keyhole tombs
- Ancient Lotus Garden — lotus plants grown from 1,400-year-old seeds bloom in a dreamlike landscape (July–August)
- Gyōda Jelly Fry and Furai — beloved local B-grade gourmet: okara-based fritters and a unique okonomiyaki-style dish
* Opening hours and admission fees are subject to change. Please check the official website before visiting.
Nearby Castles
小田原城
National Historic SiteOdawara Castle
Lord: Hōjō Ujiyasu / Ōkubo clan
江戸城（皇居）
Special Historic Site / National Historic Site (Imperial Palace East Garden)Edo Castle (Imperial Palace)
Lord: Ōta Dōkan / Tokugawa shogunate
水戸城
National Historic SiteMito Castle
Lord: Edo clan / Satake Yoshinobu / Mito Tokugawa clan