There were three hills called Okayama, Ishiyama, and Tenjinyama near the site where present-day Okayama Castle is located along the Asahi River. It was Ukita Naoie who acquired the castle on Ishiyama and made it his headquarters, bringing the Okayama area to the forefront during the Warring States period. His son, Hideie, determined to place Honmaru (main enclosure and keep) on the hill of Okayama and built Okayama Castle that stands to the present day. (It is said that the Tenshu (castle tower) was completed in 1597.) According to documents from the Edo era, the castle was built under the instructions of Toyotomi Hideyoshi. In addition, the branching channels of the Asahi River were devised as they are today to protect the north and east sides of the castle and utilized to create moats, and a castle town was built that stretched long in the north-south direction between the moats. In this way, the prototype of the city center of present-day Okayama City was established, laying the foundations for the name of the city and prefecture. Later, the castle and the castle town were further expanded by successive castle lords, Kobayakawa Hideaki and the Ikeda Clan that continue to this day.