You are probably familiar with the Inca Empire, and yes, that is me on a recent trip. And at the time of the Inca Empire, it is believed that it was possibly the largest empire on the Earth at that time, incredibly complex structures and social structures they had. Now, what's often less talked about are things like the Mississippian culture, which was in North America, right over here. The Mississippi River is named for them. This is their famous city of Cahokia, near St. Louis. And in that peak, it would have 40,000 people in it. Around the world at that time, at the time of the Mississippian culture, there weren't many cities in the world that had 40,000 people.