Tatsuno Castle is not a single fortification but rather a complex consisting of two parts: a mountain fortress located at the summit of Mount Keirozan and a flatland-mountain castle situated at its base. The mountain stronghold was built around 1499 by Akamatsu Murahide. During the Muromachi period, the Akamatsu clan was an influential family that, at the height of its power, controlled the provinces of Settsu, Harima, Bizen, and Mimasaka. Murahide’s ancestors were directly involved in the events of the Genkō War in the 14th century and in the subsequent establishment of the Ashikaga shogunate. However, by the 15th century, due to the process of gekokujō, the clan began to lose its position under pressure from rising families, including their former vassals—the Urakami and Bessho clans. In addition, the Akamatsu faced constant pressure from the Amago clan of Izumo Province.
Takamatsu Castle was founded by Ikoma Chikamasa (1526–1603), who was appointed ruler of Takamatsu by Toyotomi Hideyoshi in 1587. The following year, Chikamasa began construction of the castle on the coast of the Inland Sea (Setonaikai), completing it by 1590.
During the Kamakura period, Sabo Tokitsuna, the sixth son of Sasaki Sadatsuna, built a fort on Mount Sawayama. This fort occupied a strategically important position because it allowed control over traffic along the important Tōsandō route, which was later known as Nakasendō. This road connected the capital, Kyoto, with the eastern regions of the country. Due to its location, the fortification held great military importance, and during periods of civil war it repeatedly became the site of fierce battles.
It is believed that the first structures on this site were built by Tachibana Akitoshi (?-1568), head of the Tachibana clan, a branch family of the Ōtomo clan, as auxiliary fortifications for Tachibanayama Castle. In 1587, Toyotomi Hideyoshi established control over the island of Kyushu and granted Chikuzen Province to Kobayakawa Takakage, one of the leading vassals of the Mori clan. Takakage began construction of a new castle on the site of the existing fortifications in 1588. The exact date of completion is unknown, but by the time the invasion of Korea began in 1592, the castle had already been finished, as records note that Toyotomi Hideyoshi stayed there overnight on his way to Hizen Nagoya Castle, which served as the headquarters of the invasion forces.
The founder of the castle is considered to be Satake Yoshinobu (1570–1633). Yoshinobu was one of the six great generals of Toyotomi Hideyoshi. During the Odawara Campaign of 1590, he took part in the siege of Oshi Castle under the command of Ishida Mitsunari, with whom Yoshinobu developed a good relationship.
Kawanoe Castle is located on the small Wasi-yama hill near the port area of the Kawanoe district in the city of Shikokuchuo, occupying a central position along the northern coast of Shikoku Island. Kawanoe was also known as Butsuden Castle. The term “butsuden” in Japan refers to temple halls, and for this reason it is believed that a Buddhist temple once stood on the site before the castle was built. Due to its location at the junction of four provinces on Shikoku Island, Kawanoe held significant strategic importance and was repeatedly targeted by rival forces seeking military control over the region.
