Why? Roman Numerals

Roman numerals originated from ancient writing of the Roman alphabet, but were not always so widely recognized. They were differnt according to the places they were being used, and its individual alphabet. Although used commonly now, they were not when they were first invented. In fact, shepard's were the most common people to use it, on their talley sticks. The numeral I actually comes from the notch on the stick, not a letter in the alphabet.

http://en.wikipedia.org/wiki/Roman_numerals