Roman numerals

Roman numerals are a method of writing numbers employed primarily by the ancient Romans. It place of digits, the Romans used letters to represent the numbers central to the system:

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

Larger numbers can be made by writing a bar over the letter, which means one thousand times as much. For instance V¯ is 5000.

Other numbers were written by putting letters together. For instance II means 2. Larger letters go on the left, so LII is 52, but IIL is not a valid Roman numeral.

One additional rule allows a letter to the left of a larger letter to signify subtracting the smaller from the larger. For instance IV is 4. This can only be done once; 3 is written III, not IIV. Also, it is generally required that the smaller letter be the one immediately smaller than the larger, so 1999 is usually written MCMXCIX, not MIM.

It is worth noting that today it is usually considered incorrect to repeat a letter four times, so IV is preferred to IIII. However many older monuments do not use the subtraction rule at all, so 44 was written XXXXIIII instead of the now preferable XLIV.

Title Roman numerals
Canonical name RomanNumerals
Date of creation 2013-03-22 12:57:31
Last modified on 2013-03-22 12:57:31
Owner Koro (127)
Last modified by Koro (127)
Numerical id 8
Author Koro (127)
Entry type Definition
Classification msc 01A20