Roman numerals are part of the ancient Roman number system that remains in use today. The history of Roman numerals dates back to 1st millenium BC when they were used as to record numbers in stone, art and coins. Today they tend to be used for list items, watch and clock faces, chapter headings, copyright dates and to denote film sequels.
Roman numerals add a classic style that arabic numerals cannot. Arabic (decimal) numbers ( 0 to 9 ) were introduced into Europe about 900 AD and were adopted quickly for their convenience and mathematical ease of use.
Lists and tables can help us today with converting Roman numeral numbers to decimal numbers and there is a converter here to help.