A castle is a defensive structure built to defend against enemy attack. From ancient fortresses and castle towns, feudal lord residences and hill castle or forts of the Middle Ages, or also temple towns surrounded by a moat to fortresses built in various places at the end of the Edo Period (1603-1868), the word castle includes many meanings. From all of these, the majority of castles regarded as castle-like were those built in the almost half century from the end of the Warring States period, through the Azuchi-Momoyama period, and into the beginning of the Edo period. During this period the number of big and small castles in Japan reached over 3,000. However, following the summer campaign of the siege of Osaka in 1615, the Tokugawa Shogunate instigated the ‘law of one castle per province’ and the number of castles quickly fell to just 170. Following this, the construction of new castles and the restoration of old ones were prohibited without permission from the Shogunate, and as such the number of castles did not change much as Japan headed into the Meiji Restoration (1868-1912). As the rule of the samurai came to an end in the Meiji Restoration, the new Meiji Government released the ‘order for abandoning castles’ in 1873, and by around 1874 or 1875 about two thirds of Japan’s castles had been demolished. Following this, many castles suffered great damage during World War II. After the war, the historical value of Japan’s castles was reconsidered, and as an outstanding sightseeing resource many castle towers, turrets and castle gates that were lost to fires were reconstructed or restored.
The period of conflict of the Northern and Southern Dynasties saw the birth of mountain temples being used as castles. These became a base for guerilla warfare’s show of power, and following this changed to an area’s regional lord residence or local samurai lord’s residence, and the development of hill castles gradually followed. In the Muromachi period （1336–1573） hill castles became to be common defenses of the residences of feudal lords with slopes of 100 – 200 metres, and as Japan entered the Warring States period these castles gradually grew in scale.
As territory became unified by the daimyo of the Warring States period, and as vassals and commercial and industrial men began living in larger groups, the strategic point of the hill castles became insufficient. The Low hills or the hilly areas of plains areas at the foot of mountains where there were wide plains were chosen, and it became common for castles to be constructed into castle towns.
From the end of the Warring States period until the beginning of the Edo period each daimyo’s domain became larger. Because of this, in the construction of castles or castle towns political, military and economic optimization were desired, and wide open plains were chosen. Hideyoshi Toyotomi’s Osaka Castle is considered as the first representative example of a real plains construction castle in Japan.
Subsections in the castle partitioned according to role and function.
Honmaru (inner citadel)
The compound in the center of the castle was where the headquarters were located during times of war. In castles from the period from the end of the Azuchi-Momoyama period until the Edo period it was usually prepared as the castle lord’s residence or as the tower and palace of the government office.
Ninomaru (second citadel)
At the compound that directly defended the inner citadel, it is common to find examples the castle lord’s residence built here, and it was usual for storehouses such as those for weapons and provisions to be lined up here.
Sannomaru (third citadel)
At the compound that directly defended the outer citadel and indirectly the inner citadel, in castles from the period from the end of the Azuchi-Momoyama period （1573–1603）until the Edo period it was common for the residences of vassals and riding grounds to be placed.
As the scale of the inner citadel grew and castles crowded the land, a small compound that acted as a strong point as a last entrenchment and as the headquarters at times of war became required. For that purpose, a division of the inner citadel was constructed and was known, among other names, as the ‘tsumenomaru’, the ‘tsumenoshiro’ or the ‘tenshu-kuruwa’. Also, independent compounds within the castle known as the western citadel, the northern citadel, and the eastern citadel were arranged. In some instances a refined atmosphere like a ‘Yamazato-maru‘ was built for tea ceremonies. Furthermore, to protect the water supply the ‘Mizunote-kuruwa (Ido-kuruwa)’ was essential.
The moats, earthen and stone walls are a castle’s basic defense. The earthen walls are built from a heaped up soil. The stone walls are built instead of earthen walls and are made from stone. Stone masonry techniques include ‘nomen-zumi’ style, where non-quarried, natural stones like used in old style castles, rock faces and corners that had been processed arranged on the face of the wall, ‘uchikomi-hagi’ style where the space between two rocks filled with filler rocks, and ‘kirikomi-hagi’ style, where cut rocks with no gap in between piled up on each other. In castles from the Warring States period until the Azuchi-Momoyama period （1573–1603）, the non-quarried, natural stone style was most common, but castles built in the Keicho period (1600–1615) following the Battle of Sekigahara, the ‘uchikomi-hagi’ style was most common. The ‘kirikomi-hagi’ style became common after Japan entered the Edo period （1603–1868）.