A dam was built around the same time, a short distance from the castle, at a spot selected by a diviner, to block the waterway.

They, supported by Kanrei (Shōgun's deputy) Ashikaga Mochiuji, were in their prime during the rebellion of Uesugi Zenshū, which lasted from 1415 to 1417.

However, roughly 40 years later, the Toshima took part in the 1477 Kyōtoku Rebellion, supporting the uprising of Nagao Kageharu.

They were defeated by the army of Ōta Dōkan, a vassal of the Uesugi clan, who put down the rebellion.

Based on what digging has revealed, it has been difficult to determine the exact location, size, and extent of the fortifications and the moat.