The rise of civilization is sometimes defined as the urbanization of humanity. The transition from hunter-gatherers to living in settlements was a fundamental transformation of human society and allowed for advanced social institutions such as kings, priesthoods, and standing armies. Since then, our settlements have gotten larger and larger, resulting in the megalopolises we have today. Learn more about the cities which held the distinction of being the largest in the world. Learn more about your ad choices. Visit megaphone.fm/adchoices