Japanese castle

Japanese castles, known as *shiro* when standing alone and *jō* when attached to a name (like Ōsaka-jō), were fortresses built mainly from wood and stone. They grew out of simple wooden stockades used in earlier times and reached their classic form in the 1500s. These structures were placed to protect key locations—harbors, river crossings, and road junctions—and nearly always used the surrounding landscape as part of their defenses.

Although they were made to be durable and used more stone than most Japanese buildings, wood remained the primary material. This made them vulnerable to fire and destruction, especially during the Sengoku period (1467–1603), when many were first built. Many were later rebuilt, either later in that same period, during the Edo period (1603–1867), or in modern times as heritage sites or museums. Today, over one hundred castles survive, either fully or partly, in Japan; historians estimate there were once about five thousand. Some, like Matsue Castle (from 1611), still have their original main keeps and other buildings, never damaged by sieges or other attacks. Kōchi Castle's original main keep was destroyed by fire in 1727 and rebuilt in 1749, so its current keep is a reconstruction, not original from 1611. Hiroshima Castle, by contrast, was destroyed by the atomic bomb and rebuilt in 1958 as a museum, though much of its original stone walls remain.

Originally designed as military defenses, castles were placed along trade routes, roads, and rivers. Over time, they also became centers of government. By the Sengoku period, they served as homes for daimyo (feudal lords), meant to impress and intimidate rivals through their size, architecture, and elegant interiors. In 1576, Oda Nobunaga built Azuchi Castle, Japan’s first with a *tenshu* (main keep). This design inspired Toyotomi Hideyoshi’s Osaka Castle and Tokugawa Ieyasu’s Edo Castle. Azuchi acted as both Oda’s lavish home and his governing center, and it was placed strategically near Kyoto, giving him control over enemy transport and communication routes.

The *tenshu* served as a storehouse in peacetime and a fortified tower in wartime. The daimyo’s offices and residences were usually in single-story buildings near the *tenshu* and surrounding *yagura* (turrets). The exception was Azuchi-Momoyama Castle, where Oda Nobunaga himself lived in the *tenshu*.