just recently, in another subreddit, i saw a post where one guy made fun of a movie poster that used IIII for the number 4.
then another poster claimed that "The Romans did use IIII and IV is a relatively new phenomenon"
the only results Google is giving me are clock-related, so i don't know if that counts, though wikipedia seems to corroborate the claim, but doesn't go into detail.

did they start with IIII and then move on to IV, (if so, is there a specific point in time) or were both used whenever they felt like it?