The art of ninja fighting was passed down from father to son, or from master ("sensei") to their best students. But in the middle of 17th century, Nakagawa Sosuntzin created a ninja school in the Mutsu Province. It was called Nakagawa-ryu and taught the ninjitsu method of fighting. Nakagawa Sosuntzin himself trained a group of 10 men, which he called Hayamiti-no-mono (men of the short hit). Ninja were taught many more things than a samurai. They had to be skilled at handling swords, spears, bows and many other weapons; but also they had to know about explosive and poisonous substances, to be a good path finder and to survive in different situations. Usually they were trained from young age and had to keep a very specific physical shape. Ninja were not allowed to be too light or too heavy. A ninja who could read and write was very appreciated. 