The Ezo (northerners) group, that is, barbarians, who were in custody as prisoners in each region after the war for conquest of the north-east region, were first made by zuryos to be the private armies who were in charge of suppression and good at cavalry attack.
当初、受領たちは東北制圧戦争に伴って各地に捕囚として抑留された蝦夷集団、すなわち俘囚を騎馬襲撃戦を得意とする私兵として鎮圧に当たらせた。