Saiki occupies the alluvial delta at the mouth of the Bansho River, on the south border of former Bungo Province.

[7] Mori Takamasa, an old retainer of Hideyoshi, was given control over the Saiki territories, along with the Hita and Kusu regions of Bungo.

He defeated to the Eastern Army shortly after the Battle of Sekigahara at the persuasion of Tōdō Takatora and through his intercession was relocated by Tokugawa Ieyasu to a 20,000 koku holding in Bungo Province in 1601.

In this upper terrace there is a 20 meter square foundation of the three-story tenshu, which was lost by fire just after about 15 years from construction.

Part of the Sannomaru Palace was relocated to Funato-cho in the city as a district meeting place and still exists today.

The castle site is located a 20-minute walk from Saiki Station on the JR Kyushu Nippo Main Line.