Long before the world counted using base 10 — namely using the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 to represent all numbers — most civilizations looked to the stars to measure their world. Around 3000 B.C., astronomers in Mesopotamia developed a base 60 system while studying the sun moving around the Earth, said Jeffrey Oaks, a math professor at the University of Indianapolis. Years seemed to have 360 “parts,” as did circles (now called degrees), these early astronomers noted; 360 was a multiple of 60, and thus a base 60 system could easily represent the number.

Because astronomy was the prevailing field of science at the time, Oaks added, the base 60 system made its way from Mesopotamia, after the Persian empire conquered the region, to the Middle East, Greece, and India.

But as time passed, this number system didn’t always work. Though base 60 could help quantify the moon and the stars and days and hours and minutes, there was much more to the world. And so it wasn’t Roman numerals from present-day Italy or base 60 from present-day Kuwait and Iraq that soon became the norm: it was a numeral system from the Indian subcontinent that Arab mathematicians helped popularize. Yet, if you ask many people, they couldn’t tell you why they count the way they do.