Most know Roman Numerals as these:
but earliest in their history they looked like this:
What I find neat about these versions of the numerals is one can easily imagine the logic the original inventors of this number system used; using an extra tally mark to indicate 5, a different tally mark to indicate 10, modifying 5 and 10 to get 50 and 100, and modifying 100 to get 1000 and then chopping the symbol in half to indicate 500.
There’s also enough evidence from Roman writing to trace the evolution of the symbols to the final forms:
This diagram is adapted off of Georges Ifrah’s book The Universal History of Numbers. There are “side branches” (especially with 1000) but I kept only the elements of the most direct route to the finish.