"So, when exactly do ninjas show up in the historical record? Do they ever? They do. And it seems the earliest reference to a band of ninja occurs in the Taiheiki, written around 1360 and referring to an event which took place in 1338. And unfortunately, it's an unmitigated disaster -- the ninjas are discovered before the raid is even carried out and they are slaughtered to a man. Not an auspicious beginning! From that point, references to ninja activity increase in the histories and romances written at the time, with ninja activity finally coming into its own during the age of Sengoku, when all of Japan was plunged into war, a state of affairs which lasted throughout the sixteenth century, with the most ninja activity seemingly occuring around the Iga and Koga provinces."