The Roman numeral system is an ancient way of representing numbers. The symbols are I, V, X, L, C, D and M.

The Roman numeral system is an ancient way of representing numbers. The symbols are I, IV, V, IX, X, XL, L, XC, C, CD, D, CM, and M. These symbols are valued as follows:

I = 1
IV = 4
V = 5
IX = 9
X = 10
XL = 40
L = 50
XC = 90
C = 100
CD = 400
D = 500
CM = 900
M = 1000

These symbols are arranged in increasing value to create a number, where MCMDCDCXCLXLXIXVIVI = 3108. Values represented by a two values, with a smaller value preceding a larger value, such as IX, are only used once per number, while values represented by a single letter, such as X, can be used multiple times while creating a number, so MIXV is valid, while MIXIXV is not - this should be represented by MXXIII.