And this kept them safe. But doing these three things requires organization. You need to control workers and give them jobs and have taxes and do all of the things that are required for a civilization to grow. And that's where you're going to get government and religion and politics and really the fundamental building blocks of civilization. So let's talk about the city-state just for a few minutes here, kids, because it's really, really important. Now, the city-states, in a sense, are like little nations unto themselves that do share some commonalities. But some of those commonalities are really important.