Emperor Heizei
Iwate District was the northernmost of the six districts of northern Mutsu Province (六奥郡）created in the early Heian period after the conquest of the Kitakami River Valley from the Emishi tribes by the Japanese army led by General Sakanoue no Tamuramaro. The districts were named by Emperor Heizei, and the name of “Iwate” was originally written with the "kanji" 磐手, and appears in this form in the "Yamato Monogatari", compiled in the year 951. By the middle Heian period, the "kanji" had changed to its present form, although it was also occasionally referred to as ‘"Iwadenomori"' (岩出の森郡)