It didn't. IV has always been the Roman numeral; 4 is an Arabic numeral. the western world adopted the Arabic numbers because it is easier to use one symbol for each number, rather than mixing...
Iv iv mcmlxiv They should be all caps. This website changes them sometimes.
(IV) = 1000*4 = 4000
IIII is used to represent 4, usually on clock faces. The more usual representation of 4 is IV.
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