The Roman system of numerals has an admirable simplicity - though better suited to monuments than mathematics.
For numbers in everyday use just six symbols are sufficient, all of them letters of the alphabet: M (for 1000), D (500), C (100), L (50), X (10) and I (1). Numbers are constructed on the principle of repetition. Some, such as MM (2000) are therefore very simple; but MDCCCLXXXVIII (1888) is altogether more unwieldy.
Over the centuries many devices are introduced to cope with larger numbers or to lessen the repitition. The most familiar of these is the principle by which a smaller digit can be placed before a larger one to signify subtraction.
By this principle 4 can be written as IV (1 less than 5) instead of IIII; 9 becomes IX and 90 is XC. The system can even be used more than once within the same number. Thus 1919 becomes MCMXIX instead of MCCCCXVIIII. Roman numerals remain in use today to dignify monarchs (George VI somehow looks better than George 6) and occasionally as a typographical convention - 11 xi 1918, for example, to signify 11 November 1918.