Iwabitsu Castle

Iwabitsu Castle is a historic yamashiro-style mountain fortress located on Mount Iwabitsu in Higashiagatsuma, Gunma Prefecture, Japan. Originally constructed by the local Agatsuma clan around the 13th century, the structure was strategically positioned within a valley formed by the Agatsuma River. This location allowed it to control the Shinshu Kaidō, a vital highway connecting Takasaki to Shinano Province via the Torii Pass. The site currently exists as ruins and was officially designated as a National Historic Site of Japan by the central government in 2019 to preserve its cultural significance.

The castle holds substantial historical importance due to its role during the turbulent Sengoku period. After changing hands from the Saitō clan, it was captured in 1563 by the renowned warlord Sanada Yukitaka with the backing of Takeda Shingen. His son, Sanada Masayuki, later utilized the fortress as a primary base for expanding into northern Kōzuke Province. Masayuki significantly enhanced the surrounding town, transforming it into a fortified post with gates and defenses similar to his later designs at Shinpu Castle. The site is also linked to the tragic end of Takeda Katsuyori, who intended to seek refuge there before his death in 1582.

Following the establishment of the Tokugawa shogunate, the political landscape shifted, leading to the castle's eventual demolition in 1614 under the regime's strict regulations on military structures. Despite its destruction over four centuries ago, the earthworks and mounds marking the foundation remain visible today. These remnants offer insight into the defensive strategies of the Sanada clan and the region's feudal history. As a protected landmark, the site serves as a tangible connection to the era of famous samurai commanders like Sanada Masayuki and the officer Karasawa Genba.