Short or long Roman numerals?

Question

TL;DR: Is 1995 correctly written as MVM, or as something more like MCMLVL? MCMVC? MCMLXLV? MCMLXXXXV?

From what I recall from my Latin classes (European highschool...), you are not supposed to write more than 3 identical subsequent symbols. However, this rule hasn't been consistently followed in modern times from what I can tell by a little web research.

Perhaps it'd help if I knew how the Romans themselves wrote larger numerals... Would they write CLXL or CXC for 190? Something else still?

Answer 1

1995 = MCMXCV.

The rules are:

first triad: I, V, and X:
I, II, III, IV, V, VI, VII, VIII, IX, X

Then all is repeated with:
second triad: X, L, and C
third triad: C, D, and M

You can't use letters outside of their "triad": So, IM for 999 is wrong. CXC for 190 is correct, and 195 is CXCV (not CVC).

You should write numbers in decreasing order: thousands first, then hundreds, then tens, and finally the ones.

Longer scheme (also sometimes used for clocks) is:
I, II, III, IIII, V, VI, VII, VIII, VIIII, X
If you use it, you must use it for all three triads, of course.

It can be found in the courses of history of maths. (Mine was far ago and surely, is not on the Internet, sorry)