Di BAI
For more than two thousand years caoyun was the centralized transportation system used by central governments of imperial China to collect grain—an important form of tax levied on agricultural land—and transport it to locations such as capitals, the metropolitan garrison, the court, and the metropolitan bureaucracy. The caoyun system consisted of water transportation and land transportation.
The centralized caoyun system of water and land transportation was established during the Qin dynasty (221–206
