# Roman Numbers

The numbers that we use are called Arabic numbers, as the Europeans learnt them from the Arabs, although they were invented in India. Romans had a completely different number system.

Click in the first box and type in a whole positive number less than 4000. The Roman number will appear in the other box. Try different numbers, and see how the Romans would write them. If you have a Roman number and you want to find out what it is, click on the Roman box and type it in.

Enter Arabic number

Enter Roman number

 Arabic Roman 1 I 5 V 10 X 50 L 100 C 500 D 1000 M
In Arabic numbers, we only have ten symbols (0123456789) which can give any number however large, although the bigger numbers get quite long. So 1 means one, and 100 means a hundred. The symbol "1" means something different depending if it has any numbers after it.

The Romans thought in a different way. One is I, and two is II, and three is III. Five has a different symbol, V. There were different symbols for ten, fifty, hundred, five hundred and thousand. However, there were no symbols for anything higher, so they could only describe numbers up to 3999. Above this, there were various ways to describe numbers, but no generally agreed way.

The Romans combined their symbols, so VII meant 5+1+1 or seven. However, they found that VIIII was too confusing for nine, so they introduced another idea. If the I comes after the V then you add it (VI is 6). But if the I comes before the V then you subtract it (IV is four). The rule is that you are allowed to add up to three (VIII is eight), but only subtract one (IX is nine). You can also do this for larger numbers.

MDCCCLXXXVIII is 1000+500+100+100+100+50+10+10+10+5+1+1+1 or 1888

MCMXCIX is M CM XC IX or 1000+(1000-100)+(100-10)+(10-1) or 1999

You have to be good at adding and subtracting for Roman numbers! Also, you can't tell from the length of the number, how big it is (MM is 2000).

But why did the Romans choose these letters as symbols?

Well, the Romans counted on their fingers! I or II or III are different numbers of fingers held up. So what are five fingers? A whole hand, of course! If you look at a right (see right), you can see that the thumb and little finger make a V, and it's a lot easier than to draw the whole hand.

Ten fingers are both hands, and X is two V's (with one upside down).

The Romans spoke a language called Latin, and the Latin for hundred is Centum. So C stands for hundred.
What do these words mean? Century - Centurion - Centimetre - Cent - Centipede

The Latin for thousand is Mille. So M stands for thousand.
What do these words mean? Millennium - Millimetre - Millipede

Now for fifty. Fifty is half of a hundred, so the Romans took the symbol for hundred, C, and cut it in half. This makes an L, which became fifty.

Five hundred is half of a thousand, so the Romans took the symbol for thousand, M, and cut it in half the other way. This makes a (sort of) D, which became five hundred.

One place where you often see Roman numbers is on a clock face. The hours are marked as I to XII. However, there is something odd about these Roman numbers. If you look at four, it is IIII instead of IV. I think that this is because half of the numbers are upside down, since they follow the edge of the clock face round. You can get IV and VI muddled up when they're the right way up. It is even worse when they're upside down! IX and XI are not such a problem, since they are more or less the right way up. In fact, the Romans never had clocks like this, since they had not been invented.

This is the accepted modern way to count with Roman numbers. The Romans themselves were not so fussy. There is a Roman tombstone in York, England, of Lucius Duccius Rufinius, who was the standard bearer of the VIIII legion (9th), and was XXIIX years old (or 28!)

At the top of this page, when using the convertor, I tell you to type a number in which is less than 4000. Why? When we use Roman numbers today, we don't use them for big numbers, so you never see the Roman number for 5000 (and if you don't have that, then you can't write 4000). The Romans agreed on symbols for 1, 5, 10, 50, 100, 500, and 1000, but there were different symbols for 5000 and also for the bigger numbers. Here is one way the Romans wrote big numbers.

As you can see, it's getting quite messy!