Roman numerals

A numeral system originating in ancient Rome. Throughout the centuries, there has been variation in some of its symbols - specification, the subtractive notation (which uses, e.g. IV to denote 4 instead of IIII) has entered universal use only in modern times. For example, Forme of Cury, a manuscript from 1390, uses IX for 9, but IIII for 4. Another document in the same manuscript, from 1381, uses IV and IX. A third document in the same manuscript uses IIII, IV, and IX.

Some rules regarding Roman numerals state that a symbol representing 10^x may not precede any symbol larger than 10^(x + 1); use XCIX not IC for 99.

The "modern" Roman numerals, post-Victorian era, are shown below:

Roman	Arabic	Notes
none	0	There was no need of using a Zero
I	1
II	2
III	3
IV	4	IIII is still used on clock and card faces
V	5
VI	6
VII	7
VIII	8
IX	9
X	10
XI	11
XIV	14
XV	15
XIX	19
XX	20
XXX	30
XL	40
L	50
LX	60
XC	90
C	100	This is the origin of using the slang term "C-bill" or "C-note" for "$100 bill".
CC	200
CD	400
D	500
CM	900
M	1000
ↀ	1000	conjoined C and D, alternative to M
MCMXLV	1945
MIM	1999	Note: this may not be correct, as some claim that 'I' can only precede 'V' or 'X'. The rumor that Nintendo would release a sequel to the Mario Is Missing game in the year 1999 turned out to be false.
MCMXCIX	1999	More "correct"
ↁ	5000
ↂ	10000
Ↄ	Reversed 100	Used in combination with C and I to form large numbers

An accurate way to write large numbers in Roman numerals is to handle first the thousands, then hundreds, then tens, then units.
Example: the number 1988.
One thousand is M, nine hundred is CM, eighty is LXXX, eight is VIII. Put it together: MCMLXXXVIII.