Walls

The low-roofed walls like the one shown to the right are called hei, and are found throughout the castles of Japan. They were made originally of mud and reinforced with bamboo supports. The walls are fitted with small openings called sama, through which archers and gunmen could fire at the enemy. To keep stray arrows or bullets from entering the castle, sama were built with hourglass-shaped cross sections. The openings also come in different shapes, with rectangular slits for arrows and triangular or circular openings for guns.

These walls were most vulnerable to fire. In fact, fire was such a concern that those found guilty of arson were burned alive! The walls were often covered in plaster or lacquer in an effort to fireproof them; this is where these castle walls get their white color (or black color in the case of lacquer). However, even these measures could not completely protect the castle from fires, especially those started from the inside or by ligthning. Fire has ultimately caused the destruction of more casles than any other single factor.

Ishigaki

The curved stone walls we see on castles are called ishigaki, and they are literally the foundation on which most castles are built. Tenshu, yagura, and hei were all usually built atop ishigaki. Their sloped shape served several purposes--the first was to provide a stronger base to support the masive weight of the castles. The wider base also distributed the water pressure behind the stones that gradually built up over time. The increase in slope also made it progressively harder for invaders to climb as they got higher up the wall. Some say that the exact curvature and surface patterns of the walls were geometrically calculated according to trade secrets. At least one castle mason is known to have worked behind huge bamboo curtains in order to hide his work.

Ishigaki were first seen in mountaintop castles, where large walls were neither practical nor easy to build. These first stone walls were made by piling together large stones, then filling in the gaps with smaller stones to keep the wall in place. Later, when castles were no longer being built on mountaintops, stronger ishigaki were needed. This was done by first embedding the large stones into a hillside or embankment, and then filling in the gaps as usual. This method of dry construction ("dry" meaning without mortar) allowed the walls to be flexible enough not to collapse during earthquakes, which are common in Japan.

Moats

As with European castles, moats were the first line of defense for a castle. Built in rings around the castle, moats did not have to be very deep to be effective. Once the invaders crossed a moat, they would then have to climb an ishigaki straight out of the water. In addition, most castles had more than one moat, which compounded the challenge for opposing armies.