Along with writing, the growth of cities has often been a way that scholars mark the increasing complexity of human societies. In the ancient world, residents of cities generally viewed themselves as more advanced and sophisticated than rural folk — a judgment still made today. They saw themselves as more “civilized,” a word that comes from the Latin adjective civilis, which refers to a citizen either of a town or of a larger political unit such as an empire.

This depiction of people as either civilized or uncivilized was gradually extended to whole societies. Beginning in the eighteenth century European scholars described those societies in which political, economic, and social organizations operated on a large scale, not primarily through families and kin groups, as “civilizations.” Civilizations had cities; laws that governed human relationships; codes of manners and social conduct that regulated how people were to behave; and scientific, philosophical, and theological ideas that explained the larger world. Generally only societies that used writing were judged to be civilizations, for writing allowed more permanent expression of thoughts, ideas, and feelings. Human societies in which people were nomadic or lived in small villages without formal laws, and in which traditions and ideas were passed down orally, were generally not regarded as civilizations.

Until the middle of the twentieth century, historians often referred to the earliest places where writing and cities developed as the “cradles of civilization,” proposing a model of development for all humanity patterned on that of an individual person. However, the idea that all human societies developed (or should develop) in a uniform process from a “cradle” to a “mature” civilization has now been largely discredited, and some world historians choose not to use the word civilization at all because it could imply that some societies are superior to others. But they have not rejected the idea that about 5,000 years ago a new form of human society appeared.