The greatest challenge in discussing China’s foreign relations during the Six Dynasties period may be in determining what the concept of “foreign” even meant during this exceptionally complicated, cosmopolitan era. Not only was China divided—with each Chinese dynasty interacting with the others as if they were foreign countries—but, between 304 and 581, most of north China usually lay under non-Chinese rule. South China, meanwhile, had until recently been something of a frontier zone, and it continued to have a large non-Chinese aboriginal population. At the same time, characteristic elements of Chinese culture, notably including the use of the Chinese written language, were spreading to neighboring Korea and Japan, while what is today northern Vietnam could actually have been considered to be part of China. A city located near what is now Hanoi had been a major center of Chinese presence in the far south during the previous Han dynasty, and was not fully eclipsed by the rise of Guangzhou until as late as the seventh or eighth century.