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# What Are Roman Numerals?

Who invented Roman numerals? (The Romans, right?) Where did the idea come from? And why do we still use them today? Keep on reading to learn all about this ancient number system.

By
Jason Marshall, PhD,
January 25, 2013
Episode #139

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If you take a close look at the world, you’ll find that you’re surrounded by ancient history. There are lots of great examples of this, but today we’re going to talk about one example in particular that’s near and dear to my—and hopefully your—mathematical heart: Roman numerals. These ancient numbers can still be seen all over the place—on signs, clocks, monuments, and even in movie credits! But who came up with this number system? Was it really the Romans? How exactly does it work? And why is it still used for certain things? Stay tuned because those are precisely the questions we’ll be answering today.

## Where Do Roman Numerals Come From?

The story of Roman numerals actually begins way back in the distant past alongside the story of the so-called tally-bones that we talked about in the last episode called How to Add and Subtract Like an Egyptian. As you’ll recall, the story of tally-bones begins at least 30,000 years ago when people began making notches in bones as a way of counting. The problem with this method is that it doesn’t work well for large numbers since it’s tough to tell at a glance exactly how many notches you’ve carved. So, long ago, a tally-bone carver had an ingenious idea to make every fifth notch in the shape of what many centuries later would look like the letter “V.” This clever change meant that you could now quickly count-up most of the notches on a tally-bone by counting groups of 5—something like “5, 10, 15, 20, 21, 22” instead of counting each individual notch up to 22. Much faster!

But these clever carvers didn’t stop there. For every tenth notch, they decided to make a cross-cut in the shape of what would eventually become the letter “X.” That way they could not only count by fives, they could also count by tens. For example, whereas the number 12 would look like

I I I I I I I I I I I I

in the original system, these clever new carvers would instead “write”

I I I I V I I I I X I I

The beauty of this change is that you can ignore many of the marks since the “V” and the “X” tell you at a glance how many notches come before them. If you think about it, you’ll realize that with this new system, many of these symbols don’t need to be written at all. In the case of the number 12, all of the symbols before the “X” can be completely ignored. If we do that, we’re left with the symbol

XII

which, you may recognize, is precisely the Roman numeral for 12!

So that’s where the symbols that would eventually become Roman numerals came from…not from the Romans themselves, but from their ancestors. Or at least that’s what a lot of people think happened. In truth, there’s no way to know for sure if this is what really happened since this all took place a long, long time ago. But it certainly seems plausible to me.

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