The stone walls so characteristic of the Japanese castle were built on a foundation of earth covered with small stones over which were placed the larger surface stones. Except at the corners, which were fashioned of stone slabs arranged much like the corner of a brick wall, the stones were of no uniform size or pattern. Generally, however, they were wedge-shaped and were placed with the smaller end of the wedge at the surface and the larger on the inside. This arrangement held them locked in position by their own weight and made them resistant to earthquakes. It also necessitated giving the wall a curve, and records show that this was geometrically determined. The basic earthen wall was known as a doi and the finished wall of stone as an ishigaki. Since no mortar was used to hold the stones in place, free drainage of water was permitted. Nevertheless, openings for drainage were used, although they were kept small so as not to be of advantage to the enemy.
The main gate to the outside of a castle, called the otemon, was one of the strongest of the castle gates and was heavily protected. On the opposite side of the castle was the karamete or rear gate, through which prisoners were usually taken in and which was sometimes used by the defenders as a point of exit for an attack on the enemy.
The masugata was a type of double gate which proved to be very effective and was extensively used in castle architecture. It consisted of two sets of gates with a fixed enclosure between. The secondary door was situated at right angles to the first. Masu is the name for a square measuring vessel in Japanese. The advantages of the "measuring gate" were many: the enemy was not able to view the interior of the castle; men could enter or leave without having both gates open at the same time; attackers who gained entrance through the main gate were extremely vulnerable to fire while trying to enter the secondary gate; leaders could also inspect their men in this quarter. The space was fixed by Hideyoshi so that it would hold 240 men or 40 mounted cavaliers.
Strategic gates were constructed of large timbers often protected with plating of copper or iron. These important military points were always guarded by towers from which the enemy could be fired upon.
Castle towers, generically known as yagura, derived their specific names from their position or use. Corner towers, for example, were called sumiyagura. In exterior appearance they were structures of two or three stories, but the interior was divided into many levels, the topmost of these being used for observation. Since corners hampered lateral observation and provided cover for enemies, it was important that these sectors be protected.
The tamon, a long, low structure integrated into the castle wall, was ordinarily used for storage. On the inner side, it had doors leading to the castle compounds; on the outer, openings from which the enemy could be fired upon. Such structures were often built with a gate, and the combination was called a watariyagura. The arrangement provided a protected passageway directly above the gate, convenient both for crossing from one part of the castle compound to another and for shooting down upon hostile invaders. This type of tower-gate was frequently constructed as the inner part of a "measuring gate." Other towers were used for observation, for confining prisoners, and for protecting water supplies. Towers also served for such interesting purposes as moon viewing and committing suicide.
12. Measuring Gate (Masugata). This arrangement of two gates with an enclosure between provided a double line of defense.
All towers, gate structures, and upper walls were furnished with openings for firing upon attacking forces. These openings, known under the general name of sama, were of such specific types as yasama for arrows, tepposama for guns, and (although rarely) taihosama for cannons. The holes provided for arrows were rectangular, while those for guns were circular, triangular, or square. At the end of the Tokugawa period, when the use of firearms had become common, it was necessary to have three openings for guns to every one for bows and arrows.
The tops of walls not protected by other structures were usually occupied by palisades behind which trees were planted in the hope of stopping projectiles, as a means of camouflage, and as a device for concealing activities within the castle. Pine trees were most abundantly represented, since they provided cover throughout the year. Bamboo was grown for arrows and oaks for the shafts of spears.
The main structure or tower of a castle is called the tenshu-kaku. One translation of this is "guardian of the sky." We can trace the development of the main tower back to the early wooden towers used for observation. As military forces increased in number, the tower became larger and stronger and eventually came to house the military leader. With the introduction of the Tanegashima or matchlock gun by the Portuguese in 1542, it became necessary to build much stronger towers and to increase the size relative to the ever-increasing range of the gun. Cannons were also introduced late in the 16th century but were seldom used before the country was united under the Tokugawas. After the imposition of Tokugawa rule, there was no longer any occasion for their use.
To achieve elevation and to protect the main tower from fires set by enemy invaders, the rectangular base was built of stone. The supporting beams of the tower rested upon large stones on top of this base or in a cellar within the base. This constituted a departure from many other large examples of Japanese or Chinese architecture in which the beams were sunk in the ground. These bottom posts extended through several floors to a platform which supported the beams for the higher floors. Similar platforms added different levels around the perimeter of the structure. There were usually one or two extremely long posts which might extend from the bottom to the top of the tower for the purpose of giving stability to the different platforms. This structural device, however, should not be compared with the central beam of the pagoda, which is sunk into the ground and is primarily for support. Curved beams were used freely in the framework.
The room at the top of the main tower was often the most luxurious in the castle. It was floored with tatami mats and served as the post of the castle lord in time of siege. Because it functioned as an observation point, it was largely open on all four sides and was thus well lighted, well ventilated, and relatively comfortable. At the beginning of the Momoyama period, this observation floor jutted out from the tower roof, but in later castles it was contained within the gradual tapering of the tower outline. It was often surrounded by a balcony with a wooden railing and sometimes adorned with a bell-shaped window called a katomado. The principal window style in most castles was of the renji type, which consisted of vertical slats in a rectangular frame. This type of window provided good ventilation for the buildings, furnished sufficient protective cover, and afforded openings from which fire could be directed upon the enemy.
The covering for all walls except those made of stone was a type of plaster. Up to the time of Hideyoshi, the exterior walls were painted with a compound whose chief ingredient was persimmon juice. This served both as an insect repellent and as a protection against weathering. A later development was the addition of a lime covering that gave greater protection against fire and offered more resistance to projectiles. The Tokugawas used a tilelike covering of fired earth.
The walls, towers, and gates were usually topped with rows of alternately inverted, semicircular, overlapping tiles, the row at the outer edge consisting of round tiles bearing the crest of the castle owner. A lime mortar made the joints waterproof, gave resistance to wind, and protected the roof against projectiles. The roofs of the main tower and other castle buildings were usually surmounted at the ridge by pairs of mythical dolphins called shachi, the male occupying one end and the female the other. These figures, made of tile or metal and sometimes gilded, were considered as guardians against evil spirits.
Gables of several types decorated the exterior of the main tower. They included the chidori-hafu, resembling a triangle