Sasano-Ittobori is a particular style of Itto-bori (literally one-knife carvings) created in Yamagata prefecture. In the south of Yamagata is a mountain called Sasano-yama or Bamboo Mountain. According to legend, when Japan was first becoming a complete nation in terms of territory, Sasano-yama was an important frontier landmark. It was there on the outskirts of present day Yonezawa-shi, that settling Japanese faced the Ainu. Divided by mountain, the two groups lived uneasily for only a short time. About 800 AD Sakanoue no Tauramoro was dispatched by the emperor to quell the Aino. At Sasano-yama, he prayed to Senshu Kannon, the 1000 handed diety for sucess against the Ainu and used the Sasano-Ittobori as symbols for his plea. See Amaury Saint-Gilles. "Mingei: Japan's Enduring Folk Arts". Tuttle Publishing, Tokyo (1990). pp 18-19.