Understanding Roman Numerals

By Stephen Bucaro

Roman numerals are a number system that was used in ancient Rome. The system is still used today for things like the numbering of some annual sport events, like the Super Bowl, and movie publication dates (so you can't easily see how old the movie is).

The Roman numeral system uses the following symbols.

I = 1
V = 5
X = 10
L = 50
C = 100
D = 500
M = 1000

To create a number, you simply start with the symbol that has the largest value that will fit into that number. Then to the right of that symbol, write a symbol that has the largest value that will fit into the remainder. Keep adding symbols of lesser value to the right until there is no remainder. Examples of some numbers expressed in Roman numerals are shown below.

X = 10
XI = 11
XII = 12
XIII = 13

After the number XIII the rule "don't write a symbol 4 times" prevents you from writing the number 14 as XIIII. Instead you write a symbol that has the next largest value, and use subtraction, as shown below.

XIV = 14

Then we can resume our count, as shown below.

XV = 15
XVI = 16
XVII = 17
XVIII = 18

After the number XVIII, again the rule "don't write a symbol 4 times" prevents you from writing the number 19 as XVIIII. Instead you would write the number 19 as shown below.

XIX = 19

Then we can resume our count, as shown below.

XX = 20

The Roman numeral system is quite easy to use once you understand how it works. Below is an inscription on Admiralty Arch, London.

MDCCCCX

Note that this number violates the rule "don't write a symbol 4 times" rule. In this case it would be difficult or impossible to avoid writing the symbol C four times. But it's still quite obvious that the numeral translates to 1910.

MMVIII

Above is the Roman numeral for the number 2008. Note that the ancient Romans didn't have a symbol for zero. When you come to think of it, having a symbol to represent nothing in counting and mathematics is quite an amazing concept.