Textbooks detailing covert techniques used by ninja and written pledges about their secret missions were passed down for generations at the home of a ninja descendant in western Japan, according to an analysis of ancient documents found there.
Experts in Japanese history say the documents discovered in 2000 in Koka, Shiga Prefecture, are valuable because they prove that ninjutsu techniques employed by feudal Japan's mercenaries involved in such missions as espionage, sabotage and assassination were handed down to the next generations in the city.
Koka and Iga in Mie Prefecture are widely known as the home of the two most famous ninja clans. Ninja gradually diminished during the Edo Period (1603-1868).