According to
尚书·
禹贡, legendary emperor
禹 (Yu the Great) divided the known world into nine regions after taming the floods:
冀、
兖、
青、
徐、
扬、
荆、
豫、
梁、
雍. The term became a poetic synonym for all of China. Japan reused the same two characters for its southwestern island Kyūshū, which historically comprised nine provinces.
