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Hey, shortwaivers, Regina Barber here. And today on the show, we are diving into an unusual

part of life in the Inca Empire.

In the 15th and 16th centuries, this empire ruled over 10 million people in South America, covering modern day Peru, Ecuador, Bolivia, northwest, Argentina.

At the time, it was the largest empire in the world.

So as you can imagine, it had things like an extensive network

of roads, impressive architecture, it had a whole bureaucratic system to keep track of everything

that was going on. That's NPR science correspondent Nell Greenfield Boys. Hey, Nell. Hey there. So there is a way

that the Inka empire is unique. Well, maybe there's lots of ways.

But we are going to talk about one thing.

This intersection of numbers and knots, something I actually learned about last year on top of that, like, famous Inca fortress, Machu Picchu.

I am so jealous you've been there.

I have not.

I learned about these knots and numbers.

When I was talking to a researcher named Kit

Lee, she's affiliated with the University of St. Andrews in Scotland. When you're learning about

empires in school, oftentimes the way they teach them is that every empire, a big civilization

...