First was demographic change. Under the Han, the bulk of the population had been in the lower Yellow River valley. Now the colonisation of the subtropical lands of the Yangtze valley begins, filling unoccupied land, clearing hillsides and forests, draining marshes and developing and expanding the southern rice culture. China’s population rose perhaps as much as four- or fivefold between 280 and 464 CE. By the 500s, the south was the rice basket of China and a major centre of culture, with 40 per cent of the registered population now living in the Yangtze valley.
