The Roman number system is very different from ours. To start with they use letters rather than numbers and there is no zero. The system still used today is based on 7 letters: I = 1 V = 5 X = 10 L = 50 C = 100 X = 1000 All numbers can be written using these 7 letters, by combining them together and adding the values. For example: XVI is 10 + 5 + 1 = 16 Usually the letters are placed in order of size, starting with the largest values. There are 2 rules to remember; 1. put a letter after a larger one means you add it. 2. put a letter before a larger one means you take it away.