Cohorts were deployed throughout the country as the national military organization under the Ritsuryo system (a system of centralized government based on the ritsuryo codes), which began to take full effect at the beginning of the eighth century.
8世紀初頭に本格運用され始めた律令制においては、国家の軍事組織として全国各地に軍団(古代日本)を置くこととしていた。