Cities look to me to be our most characteristic technology. We didn’t really get interesting as a species until we became able to do cities—that’s when it all got really diverse, because you can’t do cities without a substrate of other technologies. There’s a mathematics to it—a city can’t get over a certain size unless you can grow, gather, and store a certain amount of food in the vicinity. Then you can’t get any bigger unless you understand how to do sewage. If you don’t have efficient sewage technology the city gets to a certain size and everybody gets cholera.
— William Gibson