The Lost City of Chan Chan | Lost Cities with Albert Lin

I'm headed to the lost city of Chanchan, once the beating heart of the mighty Chimu Empire. Is that a pyramid? I think that's a pyramid, a pyramid at Chanchan. Can I find answers inside the city walls as to why the children had to die? Built over a thousand years ago, amazingly, much of the city has survived, and I've been told to expect something spectacular.

Look at these walls; they stretch as far as the eye can see. I've got my drone up, taking a closer look right now. It looks like a labyrinth of walls. I'm using photogrammetry data with graphic modeling to rebuild the city, and these extraordinary walls—here they are, restored to their full glory. A truly awe-inspiring sight, rising out of the desert like something out of a fable. At its dazzling peak in the 15th century, the city was a bustling home to 60,000 people, about the size of London at the time, and covering 14 square miles. This is one of the greatest cities of human history. So why did it collapse so suddenly?

I'm here to meet Peruvian archaeologist Aturo Pérez, who's been working here for years. Ironically, his last name means "wall." "Anur, see? This is Chanchan. Look at all these carvings here. It looks like, uh, like digital fish. The Chimu covered the city with carvings of the ocean. Wow, look at these; they're everywhere."

But among all these artworks is one Aturo really thinks I need to see. An entire wall in the central palace is devoted to a giant mural over 170 ft long. "Wow, look at this! What is this? Fish?" Each one of these is actually a wave moving down towards the coastline. These currents—all these fish— they're going in a direction; they're traveling from south to north. They're actually following the course of a current, the Peruvian current.

But a closer look reveals that the mural also depicts a moment of great change—another current coming back in the other direction, fish swimming in the opposite way, north to south. Incredible! Is this right? Did I get this? "See, it looks like the Chimu are recording a dramatic shift in the ocean currents, and when that happens, something else dramatic happens too: a violent shift in the climate."

Were the Chimu recording a huge natural disaster on those walls? Were they chiseling a premonition of their own destruction? I need to check the data to see if they were right. This is a dry, arid desert, but a sudden switch in the Pacific Ocean current can trigger violent change and devastating rain. But look at this—everything flips because the ocean currents are tied to the weather currents. Everything's tied together.

I know this kind of thing; I live on the Pacific coast myself. Just in North America, this climate shift is called an El Niño. These days it happens about once every five years. About once in a generation, you get a really big or long-lasting event—that's called a super El Niño, and the impact can be catastrophic. Wait a minute, look at this. The data right here; this rainfall data.

Every year for the last decade, less than half an inch of rain—and then, boom! 2017, one big spike—four inches of rain in a single year—completely out of the blue. It happened, as recently as 2017, destructive floods in Peru caused by torrential rains triggered by a severe El Niño. Maybe there's clues in the experiences in that El Niño that'll tell me what might have happened to the Chimu.

I'm going to try to meet some people in 2017. The city of Trujillo, just three miles from Chanchan and also situated between the sea and the mountains, was one of the worst hit. I'm here to meet some people who almost lost everything. One local family filmed the flood as it tore through their home. "Never seen anything like this before. This much moving material, water just rushing down through the streets. This whole thing would have been a river."

Oh, you can actually see the storm in the background. The more I talk to people in Trujillo, the more I hear this word: "Wó." It doesn't sound like Spanish to me. "Wó is Keta, or Isketa." It's an ancient language of Peru predating the Spanish. "Wow, that's incredible! This has happened so many times for so long that there's an ancient word." It's something that's embedded in the memory: "Wó, wancha."

"Wó" is used to describe a combination of water, mud, stone, debris—coming not from the ocean in the west, but from the east in the mountains behind the city. Is it possible that the same type of event happened to the Chimu? If it did, then there must be some way of finding evidence that an El Niño event happened in their time. The answers may be up in those mountains.