More years ago than I care to admit, my math teacher told me that no Roman numerical symbol can be listed more than three time in a row. Therefore, in order to specify any number involving 4 (including forty, four hundred, 4 thousand, etc.), you have to put a 1 IN FRONT of the next whole number. E.G., the Roman numeral for 4 is IV. While I was in Rome, however, I noticed some of the old inscriptions didn’t observe this rule. So…either my math teacher was wrong or the people carving (or writing) the inscriptions didn’t understand how Roman numerals were supposed to work.
So the Romans moved on to the symbol for 5 – V. Placing I in front of the V — or placing any smaller number in front of any larger number — indicates subtraction. So IV means 4. After V comes a series of additions – VI means 6, VII means 7, VIII means 8.Source(s): romannumerals.net
Its already been said, and I suspect will be repeated more, but the answer is still IV. And to prevent any future confusion (or posts "what is number 6 in roman numerals? … 24? …427?"): http://en.wikipedia.org/wiki/Roman_numerals
No one here has given a complete answer yet.
ONE way of designating "4" in Roman numerals is "IV".
However on some Grandfather Clocks using Roman numerals, "4" is shown as "IIII" (four capital "I"s in a row)
IV. i think of it as I away from V and the higher numbers as V plus I or II and so on
well i am guessin at least 5 people will repeat this and i know at least 2 people allready have said this so there is no real reason to answer but still, here we go. IV
I = one
and V = five
so its kind of like backwards subtraction. VI is six, and X is ten