According to the Ritsuryo Code which was the fundamental law at the time, all the land in the country were, in principle, state-owned, and such public lands were allotted to common people for their cultivation (this allotment was called "kubunden"), and it was stipulated that the collection of taxes be made from their harvests (this tax was called "so").
当時の根本法令であった律令においては、原則として国の土地は全て国有地であり、公の土地を民衆へ耕作割り当てを行い（口分田）、その収穫から徴税する（租）と規定されていた。