I think it is IXIXIX. I checked the internet and that what I got but hey it might be wrong.
Improved Answer:-
In accordance with today's rules governing the Roman numerals 999 converted into Roman numerals works out as CMXCIX.
But during the Roman era the Romans themselves would have calculated the equivalent of 999 on an abacus counting device as DCCCCLXXXXVIIII and probably simplified it to IM (-1+1000 = 999) in written form.
CMXCIX.999 = CMXCIX
999
bar(bar(CMXCIX)CMXCIX)CMXCIX
IM represents 999 in Roman numerals (-1+1000).
In Roman numerals, 999 million and 999 is represented as CMXCIXMCMXCIX. The breakdown is as follows: 999 million is CMXCIX followed by an "M" for million, and 999 is represented as CMXCIX. Thus, the complete representation combines these two parts.
CMXCIX.999 = CMXCIX
999
bar(bar(CMXCIX)CMXCIX)CMXCIX
IM represents 999 in Roman numerals (-1+1000).
In Roman numerals, 999 million and 999 is represented as CMXCIXMCMXCIX. The breakdown is as follows: 999 million is CMXCIX followed by an "M" for million, and 999 is represented as CMXCIX. Thus, the complete representation combines these two parts.
The number is 99 trillion 999 billion 999 million 999 thousand 999
The Roman numeral IM means -1+1000 = 999
999 is IM Roman numerals = 1000-1
Notwithstanding todays modern conversion of 999 into Roman numerals which is now considered to be CMXCIX inasmuch that the ancient Romans would have probably added together the equivalent of 777 and 999 in either of the following formats:- Abridged format: DCCLXXVII+IM = MDCCLXXVI => 777+(1000-1) = 1776 Elongated format: DCCLXXVII+DCCCCLXXXXVIIII = MDCCLXXVI => 777+999 = 1776 QED
IM in Roman numerals represents 999 (-1+1000).
In todays notation of Roman numerals they represent: 999
888 when writing with roman numerals it is 12 characters long DCCCLXXXVIIIAnother answer:999 in Roman numerals in additional notation is DCCCCLXXXXVIIII which has 15 numerals.