1	5	10	50	100	500	1000
I	V	X	L	C	D	M

The numeric system represented by Roman numerals originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers in this system are represented by combinations of letters from the Latin alphabet. Roman numerals, as used today, employ seven symbols, each with a fixed integer value, as above.
The use of Roman numerals continued long after the decline of the Roman Empire. From the 14th century on, Roman numerals began to be replaced in most contexts by the more convenient Arabic numerals; however, this process was gradual, and the use of Roman numerals persists in some minor applications to this day.
For more information on how the numbering system works and the history behind it please refer to the wikipedia page.

1	2	3	4	5	6	7	8	9
I	II	III	IV	V	VI	VII	VIII	IX

 

10	20	30	40	50	60	70	80	90
X	XX	XXX	XL	L	LX	LXX	LXXX	XC

 

100	200	300	400	500	600	700	800	900
C	CC	CCC	CD	D	DC	DCC	DCCC	CM

 

5,000	10,000	50,000	100,000	500,000	1,000,000
V	X	L	C	D	M