Oka Castle is classified as a mountain castle, and is located in Ōita Prefecture. During the pre-modern age, it found itself within the borders of Bungo Province. It is associated with the Ogata, Nakagawa clans. Dates in use: 1185 - 1871.

Few castles in Japan have had as long a history as this one. Oka castle was built and expanded upon in stages over a period of almost 500 years and was initially a castle aligned with the Minamoto clan during their battles with the Taira. The remnant stone walls & foundations stretch for several kilometres.

There was once a turret called the Suzumi (Cooling Oneself) Yagura for the ladies of the castle. Other buildings included, the main tower - Gosangai Yagura, the Tsukimi Yagura and the Ofuro Yagura.

Timeline

1185	Said to have been constructed by Ogata Saburo Koreyoshi.
1300's	During the mid 1300's, the castle was granted to, and repaired by, the Shiga clan who were subordinate to the Ōtomo clan.
1586	The castle garrison, under the command of Shiga Chikayoshi, resisted the attacks of the Shimazu clan.
1593	The Ōtomo had their lands, and thus that of the Shiga's confiscated.
1594	The Nakagawa clan were transferred here and remained for 14 generations. The castle was remodeled over the following two years.
1663	The castle was enlarged with the addition of the Nishi no Maru making it a truly giant mountain castle.
1769	The Sankai turret (三階櫓), the castle's de facto Tenshu, collapsed due to an earthquake.
1771	The majority of the castle's building were lost to fire. The fire had originated in the castle town.
1774	The three-layered tower (三階櫓) was rebuilt.
1871	The castle was decommissioned.
1874	A vote took place that the buildings of Oka castle, along with those of four other castles in Ōita, be torn down and their materials be used for other building projects.
1926	Designated a National Historic Site.

Historical recognition

Site	National Historic Site