Romans used a device called a "calculator" which was a flat plate with vertical channels cut or pressed into it. It resembles what we would now call an "abacus"

Romans used a device called a "calculator" which was a flat plate with vertical channels cut or pressed into it. It resembles what we would now call an "abacus". get rid of the subtractive rule, and roman numerals are just a way of writing the state of a calculator, with each letter representing a calculi, and the value of the letter representing which column it is in. most abacuses are base 10, with a special segment in each column for a stone that represents "5" in that position. Thus, each roman numeral is either a power of 10, or half a power of 10. with that context in place, the method of writing it isn't a positional system, exactly, but it's a way of serialising a positional system by capturing positions by naming them explicitly. edit: here's an image of a replica calculator, note how the columns are labeled. https://i.pinimg.com/originals/9c/79/d6/9c79d6681331953e09be687599300022.jpg https://i.pinimg.com/originals/9c/79/d6/9c79d6681331953e09be... edit2: it’s also easy to see in this context how this relates to our system of money, and coin values and names such as “cent”, if roman numerals aren’t decimal then neither are coins.