Iga-ryū 伊賀流 (literally “the Iga School”) is a school of ninjutsu. It became one of the two most well-known ninja schools in Japan, along with the Kōga-ryū. The Iga-ryū originated in Iga Province in the area around the towns of Iga and Ueno (modern Iga City in Mie Prefecture).
Members of the Iga School of ninja were trained in disguise, escape, concealment, explosives, medicines and poisons, they were trained in techniques of unarmed combat and in the use of various weapons such as shuriken and ninjatō swords. Ninja swords were shorter than the katana worn by Samurai. The ninja used scaling hooks for climbing and supposedly used special "water-walking shoes" (which are displayed at the Iga Ninja Museum at Iga-Ueno).
The ninjas of the Iga-ryū were divided into three classes: high ninjas (Jonin), middle ninjas (Chunin) and low ninjas (Genin).
Being a secretive society where stealth was highly valued, the origins of the Iga Ninja are shrouded in mystery. Some have postulated a foreign influence (Chinese) in the origins of ninjutsu others speculate about defeated soldiers retreating to the hills and adopting survivalist techniques.
It was during the early Muromachi period, that the people of the Iga region became effectively independent from their feudal overlords and established a kind of republic in their region. The Iga Republic was called Iga Sokoku Ikki (伊賀惣国一揆) in Japanese. Iga-mono 伊賀者 (Iga-men) first appear in historical records in 1487 when the Shogun Ashikaga Yoshihisa attacked Rokkaku Takayori, the daimyo of southern Omi Province. Both Iga and Koga ninjas fought on the side of Rokkaku helping to successfully repel the Shogun’s attack. Iga-mono is a synonym for Iga Ninja. In 1579 warlord Oda Nobunaga’s son Oda Nobukatsu launched an attack against the Iga Republic but was defeated by local troops and ninjas mustered by the people of Iga. Oda Nobunaga could not let his family’s loss of face to a band of ninja stand unanswered. So in 1581 he launched a massive invasion of Iga, attacking from six directions with a force of 40,000 to 60,000 men. The Iga fought bravely but were soon reduced to holding out in two castles. However, after ruthlessly slaughtering many Iga Ninja and their family members, Oda Nobunaga then declared a cease-fire and allowed some of the ninja to escape. The castles were surrendered to the warlord.
In 1582 Hattori Hanzo, offered the future Shogun Tokugawa Ieyasu an escape route which passed through Koga and Iga regions to enable his return to the province of Mikawa. This was during the turmoil following Oda Nobunaga’s death.
Ieyasu, when he became Shogun, employed ninja to guard the Edo Castle, the headquarters of the Shogunate. He settled 200 men from the Iga-ryū in the Yotsuya neighbourhood of Edo (Tokyo). Iga men were employed to guard key gates of the castle and were used as intelligence agents for the Shoguns. The west gate of Edo Castle is called Hanzo's Gate because the residence of the Hattori clan was near the gate.
Hattori Hanzo’s son Hattori Masanari was commander of the Iga guards at Edo Castle but he proved to be a less successful leader than his father when in 1606 the Iga men rebelled against him due to harsh treatment.
Iga Ninjas continued to be employed by the Tokugawa Shoguns until Tokugawa Yoshimune (ruled 1716-1745) dismissed all ninja from intelligence work and replaced them with people from his local Kii Province. The local people then reigned until the next powerful general (kia tukanara) arrived.