Roman numeral

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A Roman numeral is the name for a number when it is written in the way the Romans used to write numbers. Roman numerals are not used very often today in the west. They are used to write the names of kings and queens, or popes. For example: Queen Elizabeth II. They may be used to write the year a book or film was made.

1 The base
2 Writing numbers
3 Notation
4 What they are used for

[edit] The base

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

If a lower value symbol is before a higher value one, it is subtracted. Otherwise it is added.

Therefore 'IV' is '4' and 'VI' is '6'.

For the numbers above X, only the directly preceding symbol may be subtracted: 99 is therefore: XCIX (and not IC).

[edit] Writing numbers

Numbers are written as Roman numerals in this way:

I = 1 II = 2 III = 3 IV = 4 V =5 VI = 6 VII = 7 VIII = 8 IX = 9 X = 10

XI = 11 XV = 15 XVI = 16 IXX = 19 XX = 20

XXX = 30 XL = 40 L = 50

LX = 60 LXI = 61

XC = 90 C = 100

CD = 400 D = 500

CM = 900 XM = 990 M = 1,000 XM = 990

[edit] Notation

The System that is in use today is as follows: Whenever the same symbol is encountered four times, it is replaced by subtracing it from the next higher (5,50,500). That way, IV is written instead of IIII (4), XL instead of XXXX (40), etc.

Usually only one number is subtracted, not two. 8 is therefore always VIII and never IIX

Especially on clocks and watches, IIII can sometimes still be found.

[edit] What they are used for

In the Baltics and Russia, the days of the week, are often written as roman numbers, I being Monday.
When writing dates by hand, the month is sometimes written as a Roman numberal.
When films or books are published, the year of publication may be done as a roman numeral.
When people talk about Monarchs or Popes, Patriarchs, or other leading figures, they are sometimes counted with Roman numbers, eg. Queen Elizabeth II (of England), Pope John Paul II, Pope Benedict XVI, Patriarch Alexius II (of the Russian-Orthodox church)
In France, the trimesters are sometimes counted with Roman numerals.