The truth of Ninja -Ninja Encyclopedia-


The ways that ninjas get over a castle’s moat



In general, around Japanese castles many obstructions were prepared, the main one was the moat. In the Warring States period during a war, it was really hard for troops to raid the centre of a castle when there was a water moat around the castle. This fact applied not only to armies but also to individual agent provocateurs like ninjas because during the daytime, invaders were in full view from the center of the castle. Ninjas would die if sniped from inside but if ninjas could not get over the moat, they could never steal their targets. Ninjas made ways of getting into the castle secretly and these were called " Suijutsu (水術) " .
The first most obvious method was to swim over the moat at nightime. In this case, ninjas would swim across with their clothes on. You may think that it would be more rational to do it without clothing on but actually, there was always a possibility that their enemies set traps, like setting snakes or leeches in the water. So ninjas would get in the moat without getting undressed then they would wear a big leaf on their head for camouflage and put on " Ukidasuki (浮きだすき) ". Ukidasuki means the bladder made of bowels of animals. Ukidasuki gets buoyancy by being filled with air. Naturally, ninjas had skills to overcome the coldness of the water. They painted the oil of Japanese star anise on their eyes, noses and anuses before they dived into the water and ninjas warmed up their bodies by drinking sake (酒).

Ninja's suijutsu Tools

Although ninjas had certain techniques for swimming over moats, they wanted to avoid diving into the water and revealing their true intentions because if they got wet, it would be impossible to use firearms or gunpowder. Wet clothes would make their activities after the swim difficult, and if it was too cold so issues related to their health would arise. Ninjas worked out some tools to pass a moat without getting drenched and the key ones are discussed below. Ninjas made improvised rafts called " Kame-Ikada (瓶いかだ) " . In Japanese, "Kame" means a bottle and "Ikada" means raft. Ninjas took advantage of the buoyancy of empty bottles and made a raft by means of making bottles combined with bamboo rods or timber. Ninjas would also gather cattails growing on the shore of ponds or swamps and tie them up with a rope. As a bundle of cattails can float on the water, ninjas would attach them to logs to make a makeshift raft.


The most famous Suijutsu-tool is " Mizugumo (水蜘蛛) " . In Japanese, " Mizu (水) " means water, " Kumo (蜘蛛) ” means spider. Mizugumo was introduced in the "Bansenshukai (萬川集海) ", which is an esoteric writings about ninja and ninjutsu written in the Edo-period with illustrations. Mizugumo is a loop of combined wood pieces with a diameter of about 700 mm . There have been lots of discussions about the way of using Mizugumo. Thinking about it practically, the shape of mizugumo made people believe that ninjas wore mizugumo on their right and left feet and walked on the water. However, the buoyancy of mizugumo is too light to support an adult, only a child would be light enough for them to have enough buoyancy. The second opinion is that ninjas got on one mizugumo like a boat with swimming floats and rowed it with a pole but assuming this method, it is unknown what would be used as swimming floats.
At last, the most convincing idea is that mizugumo was used when ninjas went over marshes. On the moats of Japanese castles, there are some places which are swamps. Frequently, they were the blind spots from the inner citadel. Popular opinion says that ninjas would pass through the swamp by putting on a mizugumo on their right and left feet. In this case, it is certainly possible that mizugumos supported the weight of a ninja and perhaps it was maybe a trick that the name of this tool is " Mizugumo" . As explained before, in Japanese " Mizu (水) " means water so if someone knew the name and shape of this equipment, he would think mizugumo was something for water, instead of considering it as an apparatus for swamps but this is also no more than a hypothesis.
The fact of the matter remains that the usage of mizugumo is debated and there are a number of theories.