Roman numerals
The letters used by the Romans for the counting numbers. In Roman numerals:
I = 1X = 10 II = 2L = 50 III = 3C = 100 IV = 4D = 500 V = 5M = 1000 VI = 6 VII = 7 VIII = 8 IX = 9
Numbers are represented using the shortest sequence of letters possible. The value of the letters are added, except when a smaller one precedes a larger one; then the smaller value is subtracted from the larger one. Using a combination of these symbols the Romans were able to write any counting number.

Examples:
LXVI represents 66, that is, 50 + 10 + 5 + 1.
LIX represents 59, that is, 50 + (10 - 1).