In the fourth millennium BCE, in what is known as the Yangshao culture, villages appeared, often protected by large, ditched enclosures. Then, after 3000 BCE, in the so-called Longshan period, a spurt in population growth saw an enormous number of small settlements springing up, many of them in the uplands to the west of the Yellow River plain, some with tamped earth walls that look like centres of local power.
