The Roman numeral system is a method of notation in which the capitals are modeled on ancient Roman inscriptions. The Romans were active in trade and commerce, and from the time of learning to write they needed a way to indicate numbers. The system they developed lasted many centuries, and still sees some specialized use today.

The numerals are represented by seven capital letters of the alphabet:

The Romans usually wrote IIII for 4 and XXXX for 40. The number 949 was DCCCCXXXXVIIII. To shorten the length of such numbers a "subtraction rule" appeared in later Roman times and was commonly used in medieval times. The "subtraction rule" allows the use of six compound symbols in which a smaller unit precedes the larger:

Using these symbols, 949 is written more compactly as CMXLIX. (Other "subtracted" symbols are not allowed. Thus 99 must be written as XCIX, not IC). The use of subtracted symbols was never mandatory, so IIII and IV can be used interchangeably for 4.

If a letter is preceded by another of lesser value (e.g., IX), the value of the combined form is the difference between the values of each letter (e.g., IX = X (10) – I (1) = 9).

To determine the value of a string of Roman numbers (letters), find the pairs in the string (those beginning with a lower value) and determine their values, then add these to the values of the other letters in the string:

A dash over a letter multiplies the value by 1,000 (e.g. V = 5,000).