While it may seem obvious that Roman Numerals were based on the Latin alphabet, the I, V and X are in fact common to many cultures that long pre-dated the Roman civilisation. The origin of I, V and X may be are the second oldest invention to fire! Animal bones dug up in Western Europe by archeologists used to be scratched with an I V or X to score how many animal had been killed. Tallies in caves next to animal paintings indicate very strongly that  these three symbols represented quantity long before the Roman alphabet came into existance! Knotted strings and pebbles have also been used for counting and recording quantities in various cultures.

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The Problem of arithmetic with Roman Numerals It's hard to add subtract multiply and divide with Roman numerals. Like me, I'm sure you would find it very difficult to add large Roman Numerals, let alone multiply or divide! Roman Numeral Addition                   CCXXXII +              CCCCXIII +             MCCXXXI +            MDCCCLII = MMMDCCXXVIII The difficulty of performance mental arithmetic with Roman Numerals led to the creation of the Roman Numeral abacus shown to the right. Roman Numeral Abacus

Roman numerals didn't support arithmetic as they were simply abbreviations for physical amounts. In fact business people in ancient Rome would use calculators whenever they needed work with Roman numerals. The calculator back then was the abacus. Like most other numerical systems Roman numerals were mainly concerned with addition. In the beginning, the numerals were independent of one another. One Roman numeral next to another usually meant that you would add their values together. So II was two and III was three.

Rules of Roman Numerals

Yet the Romans began to introduce silly rules. Instead of four being IIII they eventually made it IV. The Roman numeral rule was every numerical sign placed to the left of a sign of higher value is to be subtracted from the higher value. So IV meant 1 from 5 while VI still meant 5 plus 1. Therefore a digit could be both positive or negative in effect depending on whether it was to the right or left of a higher digit! 

4 = IV ( 5 - 1)                        9 =  IX (10-1)                       19 = XIX (10+10-1)                        40 = XL (50-10)          

90 = XC (100-10)               400 = CD (500-100)           900 = CM (1000-100)

Various rules also apply for subtraction with Roman Numerals.

(a) only subtract powers of ten (I, X, or C, but not V or L)
(b) only subtract one numerals from another
(c) do not subtract a numeral from another that is more than 10 times greater (ie, you can subtract 1 from 10 [IX] but not from 20. There is no such number as IXX as 19 is written XIX as shown above).

Lastly, a horizontal bar above one or more Roman Numeral multiplies its value by 1000.

Eg.              V = 5       V = 5 000                           M = 1 000              M = 1 000 000

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So while the Roman Empire came to dominate the world, their system of numbers was in reality not as good as what was to replace it. Yet just as the Romans used the principle of precedence in their system to denote subtraction from the numeral to the right, Australian Numerals use the principle of subsequence, as will be explained shortly.

Roman Numerals were superceded by the Arabic Numerals we use today. So go ahead and type a number into the box below to convert it to Roman Numerals.