How to Translate Roman Numerals
Roman numerals consist of a combination of the I, V, X, L, C, D and M letters. The position of the letters in relationship to each other is what determines the value of the actual Roman numeral. For example:
 If smaller numbers follow larger numbers, the numbers are added. For example, the Roman numeral XII calls for the addition of ten and two, resulting in the value of twelve. XII = 10+2
 If a smaller number precedes a larger number, the smaller number is subtracted from the larger. For example, the Roman numeral IIX calls for the subtraction of two from ten, resulting in the value of eight. IIX = 102
 VIII = 5+3 = 8
 IX = 101 = 9
 XL = 5010 = 40
 XC = 10010 = 90
 MCMLXXXIV = 1000+(1000100)+50+30+(51) = 1984

A Brief History of Roman Numerals
Roman numerals, as the name suggests, originated in ancient Rome. No one is sure when Roman numerals were first used, but they far predate the middle ages.
Theories abound as to the origins of this counting system, but it is commonly believed to have started with the ancient Etruscans. The symbol for one in the Roman numeral system probably represented a single tally mark of the kind people would notch into wood or dirt to keep track of items or events they were counting.
Roman Numerals in Modern Times
Roman numerals are still used today in a variety of applications. For examples:
 in outlines for a story or report
 on clocks and watches such as IV for the number 4
 in books to number prefaces, forwards and book chapters
 on films and big events such as Rocky II and Super Bowl XLVI
 for monarchs such as Elizabeth II and Henry VIII
 for popes such as Pope John Paul II
Roman Numerals in Crosswords
Crossword puzzle creators are fond of using Roman numerals in their puzzles, ranging from requiring translation of complex numbers to expecting puzzlers to know that a Roman numeral M stands for one thousand. If you want to be an expert crossword puzzler, you probably need to get familiar with the Roman numeral conversion process or keep a conversion chart handy. A typical crossword clue is "Half of MCIV" which should be answered "DLII".