The ancient Romans used letters to write numbers. These are called Roman numerals.
H = 100 000
F = 50 000
Z = 10 000
M = 1000
D = 500
C = 100
L = 50
X = 10
V = 5
I = 1
Therefore, numbers 52 is LII and 337 is CCCXXXVII in Roman numerals.
ZMM = 12 000, MMIII = 2003, MMVIII = 2008 and ZZZMMM = 33 000
But how do you write a number like 900? Wouldn’t it be inconvenient to write out nine C’s? What about 90? One L and four X’s also sounds like a lot to write out? Thankfully, the Roman numeral system has an easier way of writing numbers such as these. The letters CM mean 900. Because the C, which is the smaller value of 100, is written before the larger value of 1000, it means that the smaller value should be subtracted from the larger. Therefore CM = 900 = 1000-100. The same is true of 90, for example, which is written XC, to indicate that 10 should be subtracted from 100.
This is true of many numbers. MCMXCVIII = 1998 and IV = 4.
More about Roman numerals
The Roman numeral system was invented hundreds, and maybe thousands, of years before the beginning of the Roman civilization. The Romans inherited the system from the Etruscans. The Roman numerals we know today use the Latin alphabet. The Etruscans used some symbols that were different, but they meant the same thing. The signs I, V and X are the oldest numbers. These numerals were used to signify their respective values even before the alphabet was invented.
Roman numerals follow something called “the rule of sum” or “the addition principle.” This means that you write numbers by putting numerals next to one another. The largest number is always written to the left and numbers decrease in value from left to right.
The Romans established certain rules to make it easier to write certain numbers. One of these rules is illustrated in the example above: a smaller numeral written to the left of a larger one should be subtracted. Therefore 4 = IV.
Doing arithmetic with Roman numerals was far from easy. For example, adding CCXXXII and MCCXXXI is very difficult. This is why the Romans had to use an abacus for basic arithmetic. Our numeral system is much better. In the decimal system, the value of a number is defined by which number it is and where it is placed. They key to making this work is zero. Many people don’t realize that zero is one of the greatest mathematical inventions ever. We can thank Indian mathematicians for this invention.