> They did in contemporary depictions (Trajan's column) so this is only as much artistic license as real Roman artists would take, and for the same reason - it's more visually impressive.

The point is that Trajan’s column was propaganda. So this depiction is second-hand fiction (rehashing ancient propaganda with modern values).

The whole point of the series is that the scene is completely wrong from a historical point of view.

> Well, this wasn't typical, but you fight with the army you have

He makes the point that this was way outside the normal composition of a Roman army, not slightly off. And that as a result it would be terrible for Roman tactics and would have no hope to survive such a battle. Also, medieval siege engines in a pitch battle is just silly, there is no defending that.

I enjoyed the movie but I think that we can completely drop the assumption that it has any grounding in historical reality. It’s fiction, just slightly more realistic than Games of Thrones. Then we can appreciate the movie for the silly entertainment it is (and he does not dispute that).

> but not in 180 AD, because that specific period happens to be well-documented?

As for "why pick 180 AD then?" it's clear that this was chosen in order to have Commodus as a villain. Commodus is shown mostly historically accurately: he really was with his aging father Marcus Aurelius in Germania, he really was a teenage emperor who was seen as immature, vain and capricious (if the historical record doesn't explicitly support "downright evil") and he really did love staging ever-greater gladiator games.