The seven basic letters or symbols used in Roman numerals include I, V, X, L, C, D and M. Historians believe that the ancient Romans started using Roman numerals because they needed a common method for counting. The counting system was devised based on the human hand's 10 fingers.
Each letter or symbol has a specific meaning in the Roman numeral system. A single line, represented by what we know as an "I" was used to reference one finger or one unit. A "V" symbol represented five fingers, while an "X" was representative of two hands or 10 fingers. The Roman numeral M, which represents 1,000 units, was derived from "phi," a Greek letter that was sometimes represented as "CI" with a backwards "C" at the end, which gives the appearance of the letter "M." The Roman numeral "D" came to represent 500 units, since the shape formed by the symbol described above, "CI" followed by a backwards "C" at the end, was thought to look like the letter "D." The letters "L" for 50 units and "C" for 100 units evolved from flattened out or superimposed renderings of other Greek letters.Learn more about Numbers