Like MCXIII or something like that. Did they have to translate them in their minds first or were they like 'oh, look one thousand one hundred and thirteen'.
Follow up question: How did romans do math using their numerals? Dividing 3356 by 5 is relatively easy using just a pencil and paper. How do you divide MMMCCLVI by V?
What makes one system inherently more difficult than the other?
Related question: Roman civilization is typically portrayed as having made fewer advancements in pure mathematics than their Greek predecessors. Is this true, and if so, did the numeral system have anything to do with it?