Roman Legionaires' uniforms are inaccurate
The Roman legionaires' uniforms depicted in this history documentary is highly inaccurate.
The show's producers essentially chose the Roman legionary uniform of roughly 106 A.D. - the time of emperor Trajan - and used it throughout the entire historical depiction of the Roman empire.
This is the disappointment for people like me who own books on ancient warfare and see the artistic depictions of the changing uniforms of Rome, from the time of the Republic to the late Roman empire.
Like any army, past and present, no army keeps the same uniform over several centuries. Rome was no different. The helmets, armor, and shields were all different from the Republic through the early empire to the very late empire.
Maybe the show's producers didn't have the funds to finance accurage arms and armor and decided upon one pattern that would not be noticeable to the average layman. The Roman legionary of 350 A.D. looked very different from the classic Roman legionary at the height of Rome in 108 A.D. Towards the end of the empire, many legionaries did not even have armor, just the simpler mass-produceed multi-pieced helmet, larger shield, and long sword (spatha). I wish the director and producers had thought better to do a good job for historical accuracy.