I use a calendar to keep up with my work as a science cat. I also love calendar apps that count down to big events—like my birthday. People have always tracked time for work and holidays.

Nikolaus Overtoom.

I talked about this with my friend Nikolaus Overtoom. He’s a professor of ancient history at Washington State University.

He told me we use the Gregorian calendar today. That’s a revised version of the Julian calendar. The Romans invented the Julian calendar.

But there were calendars before that. Ancient people all over the world had calendars—including a detailed calendar made by the ancient Maya.

“Early people looked to the heavens to understand the movement of planets and stars,” Overtoom said. “They used that information to help structure their societies. They needed to know when to plant crops or move their herds.”

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