wooden walls; holes, ditches, moats, and natural barriers were the principal forms employed from early times. The fortified residence is probably the forerunner of the castle. In areas where there were large military organizations, the residences of the leaders and their supporting troops had to be strongly protected. In the two centuries preceding the rise of Nobunaga, central Japan was divided and ruled by numbers of warlords. The struggles among them brought about the further development of military architecture through the construction of larger fortresses capable of withstanding sieges by a greater number of men.
As Nobunaga gained control of large sections of the country, it became possible for him to build a castle of appreciable size and complexity. Such castles, of ever-increasing strength, continued to be built throughout the Momoyama period, and it was not until the country became completely unified and peaceful under the Tokugawas that the importance of the castle began to decline.
There are three distinct castle types, classified according to their topographic location: the sanjo or castle located at the summit of a small mountain; the hirajo, located on a plain; and the hirasanjo, located partly on a mountain and partly on a plain. The sites chosen for castles were strategic positions, often close to the sea or rivers in order to facilitate shipping and at the same time provide protection. The advantages of the mountain castle were that it gave a view of the surrounding area for reconnaissance, that it was relatively inaccessible to attackers, and that it was more likely to survive earthquakes, which are less destructive on the heights than on the plains. The disadvantages were the difficulty of building, the inconvenience of location, the problem of digging wells, and the vulnerability to typhoon winds. The castle on the plain, however, had the disadvantage of being subject to inundation. Takamatsu Castle, for example, owed its impregnability to the surrounding water until Hideyoshi used this very factor to destroy it. A large dike was raised, and the river was diverted into the moat. When the rainy season started, Takamatsu Castle was flooded and fell to Hideyoshi's forces. The combination of the castle on the mountain and the plain was most often employed in the Momoyama period since it combined the advantages of the other types.
1. Main and Subsidiary Towers (Tenshukaku and Shotenshu). The main tower, the highest and largest building of the castle, was used for observation and as a command post for military activities.
Himeji Castle
2. Moat (Hori). In Japan, as elsewhere in the world, moats played an important defensive role in military architecture.
Osaka Castle
3. Rampart across the Moat (Dobashi). Since the dobashi were guarded by gate towers, attacking forces using them were vulnerable to heavy fire.
Nijo Castle
4. Corner Tower (Sumi-yagura). This type of tower, usually of two or three stories, was designed primarily for observation and for defense of corner sections.
Osaka Castle
5. Wall Building (Tamon). The tamon, whose outer side served as part of the castle wall, was used for storage and was entered from the inner side.
Himeji Castle
6. Wall Openings for Weapons (Sama). Openings in the castle walls served for firing upon the enemy, the shape of the aperture varying with the weapon used.
Himeji Castle
7. Tower Gate (Watariyagura). This combination gate and tower provided an enclosed passage above the gate for crossing from one compound to another or firing upon the enemy.
Himeji Castle
8. Gables: Triangular (Chi-dori-hafu) and Curved (Kara-hafu). A combination of these two gable types breaks up the mass of the large castle towers.
Wakayama Castle
9. Dolphin Roof Ornaments (Shachi). Tile or metal roof ornaments of this type were supposed to guard against evil.
Osaka Castle
10. Trap Doors for Dropping Stones (Ishiotoshi). This device served to protect vulnerable corner sections against enemy forces trying to climb the walls.
Wakayama Castle
11. Windows: Vertical Slat Type (Renjimado) and Bell-shaped (Katomado). Windows of this type provided sufficient ventilation without sacrificing cover.
Himeji Castle
The plan of the fortress consisted of a number of fortified compounds. Within an individual compound there were three types of buildings: those used for combat, residence, and storage. A castle plan was made up of concentric compounds isolated from each other by ramparts, moats, or walls. The central compound contained the main tower and the residences of the most important inhabitants, while the outer ones made up the defensive positions. The magazine was usually located in the second compound. The number and the design of the compounds varied, but there were usually three to five. Round forms were seldom used because they were easier to attack than to defend. In the castle on the plain and mountain, the main compound was set on the elevation. The terrain of the castle on the plain was broken up by moats filled with water or by a river or a lake.
The compounds or courts of a castle had the general name of kuruwa. The main compound was called the hommaru; the second, the ni no maru; and the third, the san no maru. In larger castles there were also outer courts. When the plan was irregular, the compounds were given the names of compass directions, people, or significant features. The compounds were located so that if any line of defense was captured, it could be recovered from another line. The courts were connected in labyrinth fashion to make total capture difficult.
The first procedure in building a castle was to lay out ropes on the site marking off the significant features of the plan. This preliminary was known as nawabari or marking with ropes. Intricate scaffolding was used in the construction of the castle buildings and walls. Ramps supported by scaffolding were used to transport building materials to the highest sections of the castle towers. Even today the Japanese employ similar methods in the construction of their tall buildings. No nails are used in this scaffolding; the poles are merely tied together with rope.
The building of castles employed many workmen of all sorts, and the protection afforded by the castles, together with the activity centering about them, led to the development of many thriving cities. Tokyo, Osaka, and Nagoya, for example, owe their importance originally to the construction of castles.
For protecting the approaches to a castle, three types of excavation were used: areas filled with water, wide ditches,