Built in: 1466 by Oka Mitsuhiro.
The original structure was built by Oka Mitsuhiro during the beginning of Sengoku period. After the battle of Sekigahara, Ikeda Nagamasa became the lord of Ako domain, and built Odaka Castle which was the former castle of current Ako Castle.
In 1645, Asano Naganao became the lord of Ako and finish the construction of Ako castle. Ako castle became the current structure.
The one of the main character of Chushingura, Asano Naganori is the grand son of Asano Naganao. Naganori made a serious violation at Edo castle and Asano clan was abandoned.
Later, his royal Samurai Oishi Kuranosuke revenged which became the famous story of "Chushingura."
Today, several gates, moats and walls are reconstructed.