What are Roman numerals?
Roman numerals are the number system used in ancient Rome. They use seven letters: I (1), V (5), X (10), L (50), C (100), D (500) and M (1,000).
Numbers are formed by combining the letters and adding their values, usually from largest to smallest. For example, VI is 6, XV is 15 and MDC is 1,600. A letter is not normally repeated more than three times in a row, so 4 is not IIII but IV.
When a smaller value comes before a larger one, it is subtracted. IV means 5 minus 1, or 4, and IX means 9. Only certain pairs are used this way: I before V and X, X before L and C, and C before D and M. So 49 is written XLIX rather than IL, and 99 is XCIX.
Where you still see them
Roman numerals are still used on clock faces, for the names of monarchs and popes like Elizabeth II and Leo XIV, for book chapters, for movie sequels and for events like the Super Bowl and the Olympics. Film credits also often show the year of production in Roman numerals.
Did You Know?
Many clock faces show 4 as IIII instead of IV. One theory is that it looks more balanced opposite the VIII on the other side of the dial.