General Information
The large and main keeps of Kumamoto Castle stand side by side. Both were destroyed by fire before the Seinan War in 1877 and were rebuilt using concrete construction in 1960. The Kumamoto earthquakes of 2016 caused significant damage, including fallen roof tiles and shachihoko ornaments, as well as collapsed stone walls in the basement areas. As a symbol of recovery, the restoration of the main keeps was given top priority, and they were fully restored in 2021. The large keep features three exterior layers and six floors with one basement inside. From the top floor, visitors can enjoy views of Kumamoto City and the distant Aso mountains.
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Kumamoto Castle was built by Katō Kiyomasa, who was renowned as a master of military engineering.
The castle grounds cover an area of 980,000 square meters—nearly 21 times the size of Tokyo Dome—with a circumference of 5.8 kilometers. It is one of the largest castles ever constructed in Japan and is frequently ranked among the three greatest castles, alongside Edo Castle and Osaka Castle.
Kumamoto Castle was meticulously designed to withstand prolonged and powerful attacks, earning a reputation as an impregnable fortress.
It is particularly famous for its gracefully curved stone walls, known as musha-gaeshi, which were designed to make scaling the walls nearly impossible.
The Founder, Kato Kiyomasa
Katō Kiyomasa, also commonly known as Toranosuke, is respectfully referred to as Seishō-kō (the “kō” is an honorific similar to “lord”) by the people of Kumamoto. This reverence stems largely from his efforts to develop new rice fields and implement flood control measures for the benefit of the region.
He played a key role in several battles as a trusted commander under Toyotomi Hideyoshi and was later appointed lord of Higo Province (modern-day Kumamoto). His experience in castle construction during the Japanese invasions of Korea (1592–1598) further refined his engineering skills, which he applied to great effect in projects like Kumamoto Castle.
The statue of Kiyomasa portrays a brave and daring figure. However, portraits drawn shortly after his death depict a much more sensitive and cautious man. If he was indeed a person who feared death and vulnerability, it would logically follow that he would be driven to construct an impregnable castle.
The Main Towers (Keeps)
The main keeps are distinguished by their unique architectural style, featuring Chidori-hafu (triangular gables) on all four sides and a Kara-hafu (curved gable) on the top floor. The rooms inside were named according to the type of weapon stored there, such as rifles, armor, and bows. Iron spikes called shinobigaeshi were embedded in the stone walls to prevent enemy intrusion, reflecting the castle’s many sophisticated defense features.
Its Defensive Structure
Kumamoto Castle is renowned for its extensive and elaborate defensive features, which some might consider excessive. This can be largely attributed to the profound caution and military ingenuity of its builder, Katō Kiyomasa.
His extensive combat experience led him to design a fortress that was meant to be utterly impregnable, anticipating every possible method of attack.
Masugata Koguchi
The first barrier enemy warriors face is the entrance space called Masugata Koguchi. This is a square-shaped courtyard surrounded by walls on all sides. The walls are pierced with openings called sama, through which defenders can shoot arrows or firearms. This design allows attackers to be trapped and fired upon from all directions.
Takenomaru
The next barrier is the open space called Takenomaru, surrounded by high walls lined with yagura, or turrets, to shoot down enemies who reach this area. It is said that there were originally 66 yagura in Kumamoto Castle.
The third barrier is a double pathway. One path leads to a dead end, while the other passes through six Masugata Koguchi corners, exposing attackers to fire from all directions.
The Japanese term yagura literally means "arrow storehouse" (ya for arrow, kura for storehouse), though they were used to store all kinds of weapons, food, and supplies. More than just storage buildings, yagura served as vital defensive platforms and lookout towers, positioned at strategic vantage points throughout the castle grounds. They were integral components of the castle's overall military design.
Kuragari Gomon
The final barrier is the gate known as Kuragari Gomon (“Dark Passage Gate”), which leads to the main keep. This underground passage was designed to be extremely dark, temporarily blinding and disorienting invading warriors as they passed through, leaving them vulnerable to attack.
Facing the South
The defensive structures of Kumamoto Castle face south because they were oriented toward Satsuma Province, which Katō Kiyomasa viewed as his greatest concern. It is said that he also had a small escape tunnel constructed at the base of a minor tower in the northern part of the castle for his personal use.
Key Structures
Honmaru, Ninomaru, Sannomaru
The Honmaru was where the lord of the castle planned military strategy.
The Ninomaru was the residence for the lord’s family and senior retainers.
The Sannomaru was the outermost defensive area, where frontline commanders and elite troops engaged the enemy.
Takenomaru
Takenomaru is the southern defense line, featuring the long wall called “Nagabei,” which is 242 meters long.
Iidamaru 5 storied castle tower
The five-story castle tower in Iidamaru was damaged in the 2016 Kumamoto earthquake and was left precariously supported by a single remaining stone pillar.
Sukiyamaru
The Sukiyamaru Hall is believed to have been used for cultural activities such as tea ceremonies, Noh plays, and poetry readings. It was strategically monitored from a building to the south, which featured defensive openings for gunfire and stone-throwing.
Heizaemonmaru
Heizaemonmaru is located in the western part of the castle grounds, near the main keep. Originally, there were four multi-story towers in this area, but now only the Uto Yagura remains. Due to its large size and proximity to the main keeps, it is often referred to as the “Third Main Keep.”
The Uto Yagura is the only remaining tower that preserves the original foundation structure. It has three external layers, five interior floors, and one basement—comparable in scale to the main keeps. Until the early Meiji period, there were four other five-story towers in the castle. It is said that the tower was named Uto because samurai from Uto Castle—a sub-domain of Higo (now Kumamoto)—were stationed nearby.
Defense Devices
Shinobikaeshi
Shinobigaeshi (忍返し) were defensive spikes or blades, typically made of iron, installed on top of walls, gates, and at the bases of castle towers. Their purpose was to prevent intruders—such as enemy samurai or ninja—from climbing over these structures. They are a common feature in Japanese castle architecture.
Musyakaeshi
Mushagaeshi (武者返し) refers to the steeply curved stone walls designed to make it impossible for attackers—whether warriors or ninja—to scale them and reach the castle’s main keep. This defensive feature is a hallmark of Japanese castle architecture, with the walls of Kumamoto Castle being a famous example.
Ishiotoshi
Ishiotoshi (石落とし) were openings—often square or rectangular—located at the base of a castle’s stone walls, under the eaves, or in the wooden superstructure. From these openings, defenders could drop stones or pour boiling liquids onto enemies attempting to scale the walls directly below, where they were most vulnerable. They are a common defensive feature in Japanese castle architecture, working in conjunction with features like mushagaeshi (the curved walls) and sama (arrow/gun ports).
