The functions of the ninja included espionage, sabotage, infiltration, and assassination, and open combat in certain situations. Ninjutsu was more an art of tricks, than a martial art. Ninjutsu was a separate discipline in some traditional Japanese schools, which integrated study of more conventional martial arts along with shurikenjutsu, kenjutsu, sojutsu, bÅjutsu, battlefield grappling kumi-uchi
and others. Their covert methods of waging war contrasted the ninja with the samurai, who observed strict rules about honor and combat. The shinobi proper, a specially trained group of spies and mercenaries, appeared in the Sengoku or "warring states" period, in the 15th century, but antecedents may have existed in the 14th century, and possibly even in the 12th century.
