Lazy Hollywood ancient Roman history
Watching this movie, I roll my eyes at another example of Hollywood's laziness in depicting accurate time period Roman soldiers. Usually these days, a movie's costume prop department employees simply visit a Hollywood costume warehouse and borrow Roman uniforms, armor, shields, and weaponry from the time of Emperor Trajan.
I saw that there was some attempt to change the uniforms a bit, but merely cosmetic. The Roman legionaries of the early 4th century CE, that is, from 300 CE onward, looked nothing like the legionaries of Trajan's time period, 105 CE. The helmets in the movie are all time period Trajan. Helmets in 300 CE are simpler, two-piece affairs more easily mass-produced given the huge increase in the Army and the vast amount of equipment lost in the preceeding century.