This mountain castle located in the east side of Mt. Iwabitsu in present-day Higashiagatsuma-cho, Gunma Pref. was built in the early 15th century by Azuma Taro Sukefusa. It was counted as one of the 3 Fine Castles within the territory of the Takeda clan; the others are Iwadono Castle in Kai province (present-day Yamanashi Pref.) and Kuno Castle in Suruga province (present-day Shizuoka Pref.). The castle was enfeoffed later to the Saito clan, who served as a retainer of the Uesugi clan, the ruler of Echigo (present-day Niigata Pref.) district. Iwabitsu Castle was an important military bases in this region for the Uesugi clan. After the castle fell in the battle between the Uesugi clan and the Takeda clan during the Warring States period, Sanada Yukitaka, a retainer of Takeda Shingen, became the castellan. Later, when the Takeda clan became extinct, the Sanada clan managed to protect the family estate by drifting between stronger daimyo such as the Oda, the Hojo, the Tokugawa, and the Uesugi clans, and Toyotomi Hideyoshi. Eventually, they moved to Ueda Castle and Iwabitsu Castle was dismantled as per the Ikkoku-ichijo (One Castle per Province) Order in 1615. There are a lot of remains including Honmaru (the main castle) and Ninomaru (the second castle), all of which are must-see historic places for Sanada fans.
- Higashi Agatsuma-machi, Agatsuma-gun, Gunma Prefecture
- Iwabitsu Castle Ruins