Ninja (Civ3)/Civilopedia

Ninja were the "shadow warriors" of Japanese legend -- spies and
assassins who used unorthodox fighting and espionage techniques to
further their employers' ends. They practiced ninjutsu, or "the way of
perseverance", which was originally rooted in traditional Japanese
religion. One of the fundamental elements of ninjutsu is the use of
every possible advantage -- fear, darkness, terrain, poison, and
non-traditional weapons -- to achieve the desired goal. Ninja always
maintained a cover identity, usually an innocuous one, to conceal the
ninja's true profession and aid him in espionage. The ninja were
outlawed on pain of death in the 16th century A.D. by the Tokugawa
shogunate. Their high point was the Sengoku period, where the strife
and struggle between Japanese lords created many opportunities for these
violent and skilled killers, thieves, and spies.