I’ve always enjoyed using roman numerals and still am amazed how many places we see them and take it for granted.
They started out as a way to count using your hands I = one finger V= a hand with the thumb pulled out meaning five X= two hands extended, meaning two fives = ten, and so it went on . Such a simple way to count which was useful especially in a busy market place. If one or more letters are placed after a letter of greater value, you add. If a letter is placed before a letter of greater value, you subtract. So eleven became XI or nine became IX simple mathematics was exactly that … simple.
Their usesage now is more due to aesthetic reasons than functional reasons. Roman numerals convey a sense of history and timelessness, which is especially true in clocks and watches. Also used widely in astronomy still to this day.
It became a problem when you needed to work in fractions or you needed a zero or even when numbers became just too big to calculate, it just wasn’t useful anymore. Around 950 – 1000AD we adopted the Hindi-Arabic numerals we now know.