Not to take away from these masterpieces (admired them before somewhere else), but if you are at that level of painting 3D models it's quite easy to do 2D painting on flat surfaces. After all, model painting techniques are just imitations of the old masters. The designs here are - for the most part - taken from actual Roman pictures, so no creativity issue as well.
That said, mastery lies in the painter's dedication to subject and models alike. They are just spectacular to look at (if the photos are not that good).
Final note: The column is just wrong. Such things were turning markers in the circus - even if Ridley Scott envisioned them as part of the Colosseum.
