Oshi Castle

Oshi Castle, known throughout history as the Floating Castle, earned its nickname from its dramatic setting surrounded by marshes and wetlands in Gyoda, Saitama Prefecture. Built sometime in the 15th century, this flatland castle became famous not for its stone walls or tower height, but for its ingenious adaptation to one of Japan's most challenging geographic environments and its legendary defense during a crucial historical siege.

The castle's most celebrated moment came in 1590 during the Odawara Campaign, when forces under Ishida Mitsunari attempted to capture it through an innovative flooding strategy. Rather than deploy traditional siege tactics, Mitsunari attempted to breach the castle's defenses by deliberately flooding the surrounding area to overwhelm its walls. The defenders of the castle, however, successfully resisted these flooding tactics, demonstrating remarkable engineering and resourcefulness that made the castle a symbol of determined resistance during the final stages of Japan's unification wars.

The fortress's design demonstrates how Japanese builders adapted to local conditions, using the surrounding wetlands as a natural defensive system while maintaining the ability to supply and sustain a garrison. The elevated portions of the castle grounds provided refuge even during periods of high water, while the marshes themselves discouraged direct assault. This unique approach to castle design shows the diversity of Japanese military architecture beyond the famous stone-walled mountain fortresses of other regions.

Today's reconstructed castle allows visitors to appreciate how medieval commanders solved the challenge of building defensible strongholds in wetland environments. The castle's story has inspired modern retellings, including the film The Floating Castle, which dramatized its historical siege. As a designated Famous Castle, the site attracts those interested in both military history and the ingenious engineering solutions that characterized Japanese feudal architecture.

Oshi Castle is recognized as one of Japan's top 100 castles as designated by the Japan Castle Foundation, a distinction that highlights its historical and architectural importance among the hundreds of castle sites across the country. As a flatland castle, its design reflects the defensive priorities and construction techniques of its era, with origins dating to 15th c. Visitors traveling to Saitama Prefecture can explore the site alongside other regional historical attractions.