What word is always spelled wrong?
And now the digression. A couple folks left comments to the last Dad Joke pointing out that I used an unusual formulation for the number 90 - this is typically written XC, using what is called "Subtractive Notation". Here, the ten ("X") is subtracted from the hundred ("C") to denote 90.
However, the Romans were not consistent in how they represented numbers, and there were alternate methods. I used "Additive Notation" where each ten ("X") is added to the fifty ("L"): 50 + 10 + 10 + 10 + 10 = 90.
There are a bunch of examples of additive notation - Gate 5 on the Colosseum is labeled "IIIII" instead of "V". To add to the confusion, Roman inscriptions often use both notations - on the Colosseum, Gate 44 is labeled "XLIIII".
And it wasn't just Romans who did this, either. Here's London's Admiralty Arch. 1910 is represented here using additive notation instead of the more typical subtractive (MDMX):
And this discussion doesn't touch of the really weird and obscure ways of constructing numbers. To close out a really, really pedantic discussion, I'll end by pointing out that Microsoft Excel has a function to make Roman numbers for you. ROMAN ( ) will convert your number to roman notation using one of five different notations, so 499 can be representer as CDXCIX, LDVLIV, XDIX, VDIV, or ID.
Like I said, things get really weird, like the 22nd Legion using "IIXX" which caused confusion that we've seen in inscriptions (the stonemason was apparently an educated man and "corrected" the number to "XVIII". If you want to read about something really weird today, the Wikipedia article will take you down the pedantic rabbit hole.