The Romans wrote their numbers using letters; specifically the letters 'I' meaning '1', 'V' meaning '5', 'X' meaning '10', 'L' meaning '50', 'C' meaning '100', 'D' meaning '500', and 'M' meaning '1000'.

Basic combinations

Examples:
1984 = MCMLXXXIV
2014 = MMXIV

Rules:
There were certain rules that the numerals followed which should be observed:

• The symbols 'I', 'X', 'C', and 'M' can be repeated at most 3 times in a row.
• The symbols 'V', 'L', and 'D' can never be repeated.
• The '1' symbols ('I', 'X', and 'C') can only be subtracted from the 2 next highest values ('IV' and 'IX', 'XL' and 'XC', 'CD' and 'CM').
• Only one subtraction can be made per numeral ('XC' is allowed, 'XXC' is not).
• The '5' symbols ('V', 'L', and 'D') can never be subtracted.