At the Battle of Nagashino (1575), Suganuma Sadatada had served with Takeda Katsuyori during the siege of Nagashino Castle, but suffered greatly during the actual battle itself. Katsuyori himself managed to flee from the battlefield and accompanied by Sadatada, sought refuge at Sadatada’s Damine Castle. Upon their arrival, they discovered that Sadatada’s uncle, Suganuma Sadanao, supported by clan vassal Imaizumi Dozen, had defected to the Oda clan, and shut the gates on Sadatada and Katsuyori. They were then forced to escape to Busetsu Castle, about 20km away.

In revenge for this act of treason, Sadatada faked his own death, thus relaxing security at the castle. Early one morning, Sadatada and an army of loyal followers attacked the castle, capturing the fortress along with his uncle, Sadanao and Imaizumi Dozen. Both were executed in a public area near the castle along with 100 other traitors. Less than six years later, the Takeda clan were ruined. Fearing the growing strength of the Tokugawa, Sadatada left Damine Castle and retreated to Ina in modern-day southern Nagano Prefecture. Damine was soon claimed by the Tokugawa who established another branch of the Suganuma clan, and trusted vassals, as castellan.

Located on the Inakaido, an important route connecting Ina, Nagashino and Iwamura in Mino (Gifu Pref.) and Koromo (now Toyota City) and then to Hamamatsu, Damine Castle covers a square shaped area about 200m each side. Dry moats and earthen embankments surrounded the western facing front of the castle, with its many terraced “kuruwa” or baileys. The uppermost bailey, the Honmaru, was oval in shape, and contained the lord’s residence and working area, a watchtower, retainer’s quarters, guard houses, possibly stables and kitchen facilities. The eastern facing rear of the castle was not so heavily fortified, being protected by the naturally steep cliffs along the Toyokawa River far below.

Although the castle was abandoned during the Edo Period, the castle ruins remained in relatively untouched condition, allowing for research and for the reconstruction of a number of features, including the Goten palace, the watchtower, gates and fencing to create a fine reconstruction of a Sengoku Period castle.