> separate from the letters they are composed of

I didn't actually realise they're letters. To me it's distinct symbols just like 0 is a distinct ascii symbol from O.

Now that you mention it, I realise that I knew that five is V and M is a thousand or something, but the symbol for one/1, is that actually defined as a capital i and not just a line of some form? Since surely the digit for one came before the latin script