Cities, those thriving centers of trade and commerce. They are also breeders of crime, homes to numerous gangs, and places to find slums or ghettos. To officially be a city, it must also have at least one major church or cathedral. But cities are also places of culture and class, with theater, museums and the seats of most governments. Some call cities the "pearl of civilization" and to paraphrase Terry Pratchett, if this means a piece of garbage surrounded by the secretions of a dying mollusk, they could be right! How did cities come into being, how did they evolve?
Most cities are found along the shore or major trading routes. This has been true for thousands of years and all around the world. There were the ancient Egyptians along the Nile and before them Ancient Mesopotamia, all located along rivers. Rome, Paris, London, Beijing, New York, Los Angeles, New Orleans, find a major city and there will be water near by! Does water cause the evolution or is it just required?
Then cities are, and always have been major centers of commerce. Places where business takes place, where goods are processed, bought and sold. It is where the money is printed and so the government sets up there, keeping an eye on everything that happens! Is commerce responsible for the evolution of cities?
Then there is religion, always found in major cities. Are religious leaders drawn to the big cities or do the cities evolve or revolve around the religions?
Basically trade routes were established along the rivers, it was easier to float heavy loads over water that to transport it over land. At major junctions people found it convenient to meet and trade this goods. Often the trades or negotiations took days or weeks, so settlements sprang up. These settlements became more and more complex, requiring more organization and central control, thus the governments were formed. Water was needed for the people, if there was not enough, only towns became established. Bigger rivers had more transport possibilities and required bigger governments, but those required more people to manage things. As numbers grew, religions moved to where the converts were. Then cultural things were added to provide entertainment.
Thus cities evolved from simple meeting spots to small settlement to villages to the sprawling metropolises that exist today. Will they continue to evolve and become even more complex! Possibly, but possibly not. Commerce no longer relies on water and communication is now on a global scale. Religion can reach anywhere. Thus many cities are actually shrinking in numbers and size. Poorer people who know no other life are staying and preying on the wealthy and each other. Will cities evolve to breed crime? Let's hope not
But remember everything evolves and changes, or it dies!