A ninja or shinobi was a covert agent or mercenary in feudal Japan. The functions of the ninja included espionage, sabotage, infiltration, and assassination, and open combat in certain situations. They worked for the lord who hired them or who they had the duty to serve. Despite many popular folktales, historical accounts of the ninja are scarce. Historian Stephen Turnbull asserts that the ninja were mostly recruited from the lower class, and therefore little literary interest was taken in them. Instead, war epics such as the Tale of Hōgen (Hōgen Monogatari) and the Tale of the Heike (Heike Monogatari) focus mainly on the aristocratic samurai, whose deeds were apparently more appealing to the audience. Historian Kiyoshi Watatani states that the ninja were trained to be particularly secretive about their actions and existence. In the unrest of the Sengoku period (15th–17th centuries), mercenaries and spies for hire became active in the Iga Province and the adjacent area around the village of Kōga, and it is from their ninja clans that much of our knowledge of the ninja is drawn.
The skills required of the ninja has come to be known in modern times as ninjutsu, but it is unlikely they were previously named under a single discipline, but were rather distributed among a variety of covered espionage and survival skills.
Equipment and tools
Ninja utilized a large variety of tools and weaponry, some of which were commonly known, but others were more specialized. Most were tools used in the infiltration of castles. Tools used for infiltration and espionage are some of the most abundant artifacts related to the ninja. Ropes and grappling hooks were common, and were tied to the belt. A collapsible ladder is illustrated in the Bansenshukai, featuring spikes at both ends to anchor the ladder. Spiked or hooked climbing gear worn on the hands and feet also doubled as weapons. Other implements include chisels, hammers, drills, picks and so forth.
Although shorter swords and daggers were used, the katana was probably the ninja’s weapon of choice, and was sometimes carried on the back. The katana had several uses beyond normal combat. In dark places, the scabbard could be extended out of the sword, and used as a long probing device. The sword could also be laid against the wall, where the ninja could use the sword guard (tsuba) to gain a higher foothold. The katana could even be used as a device to stun enemies before attacking them, by putting a combination of red pepper, dirt or dust, and iron filings into the area near the top of the scabbard, so that as the sword was drawn the concoction would fly into the enemy’s eyes, stunning him until a lethal blow could be made.
An array of darts, spikes, knives, and sharp, star-shaped discs were known collectively as shuriken. While not exclusive to the ninja, they were an important part of the arsenal, where they could be thrown in any direction.
Explosives introduced from China were known in Japan by the time of the Mongol Invasions in the 13th century. Later, explosives such as hand-held bombs and grenades were adopted by the ninja. Soft-cased bombs were designed to release smoke or poison gas, along with fragmentation explosives packed with iron or pottery shrapnel.
Along with common weapons, a large assortment of miscellaneous arms were associated with the ninja. Some examples include poison, makibishi (caltrops), cane swords (shikomizue), land mines, fukiya (blowguns), poisoned darts, acid-spurting tubes, and firearms.
The kunai was a heavy pointed tool, possibly derived from the Japanese masonry trowel, to which it closely resembles. Although it is often portrayed in popular culture as a weapon, the kunai was primarily used for gouging holes in walls.