 Is there a lost city in the Amazon? In 1541, Francisco Orellana was the first European to cross the entire length of South America from West to East along the Amazon. He reported seeing incredible cities, millions of people, and a thriving culture. However, a hundred years later, when other Europeans got into the Amazon, they couldn't find these cities. A strong theory is that the Spaniards brought smallpox into the Amazon, and smallpox devastated the local population because there was no immunity to it. There was a massive die-off, and the cities were deserted. Within 50 years, they were completely overgrown by the jungle, and that's why they were not seen by the explorers, who came a hundred years later. But now, the forest is being cleared, and we've begun to see the traces of those cities.