What Is the Most Important Number?

In ancient Europe, there was no such thing as a zero. The numbers used by the ancient Romans were really letters that stood for certain numbers; V was 5, X was 10, and C was 100.

But in the 10th century, a number system from the East came to Europe — along with the zero. In this number system, a digit stands for a different number depending on its "place" in the number.

For instance, the 2 in 200 stands for a different quantity than the 2 in 120. But this system wouldn't work at all if it weren't for the zero, for the 200 would be just 2 and the 120 would be 12. That's why the zero may be the most important number ever invented!