Caoliang not only supplied the salary of the royal family and hundreds of officials, but also served as the source of rations for the huge garrison in the capital. Zhang Fangping, a native of the Song Dynasty, once said: "Today's situation is that the country is based on the military, the military is based on food, and the food is based on water transportation." After the Yuan, Ming and Qing Dynasties established their capital in Beijing, millions of stones of grain had to be transported from the south by water every year to maintain the lives of millions of officials and people in the capital.
The smooth flow of water transportation is directly related to the stability of the regime. Once water transportation is blocked, the capital will fall into panic. The ancients had a profound description of this: "If the third month does not arrive, the king will be worried; if the sixth month does not arrive, everyone will cry; if the first year does not arrive, the country will be in ruins." Even in the Tang Dynasty, due to famine in Guanzhong and poor water transportation, the emperor had to lead his subjects to "eat" Luoyang, the eastern capital.
