If you're so inclined to go down a rabbit hole of 100+ hours of content, I highly suggest having a listen to Dan Carlin's Hardcore History [1]. Dan is particularly interested in military history, especially ancient military history. He has an episode on Caesar's conquest of Gaul (which he argues in any kind of modern context would be called a genocide) as well as a series on the great Persian kings, called the King of Kings. This is specifically about the Achaemenid Empire talking about Cyrus II, Darius, Xerxes and the likes.
Now as Dan would say, he doesn't find scientific and technological advancements particularly interesting (from a historical perspective). Like if Edison didn't invent the light bulb, someone else would've.
What he finds far more interesting is historical events that could've completely changed the course of history and one of those was the Battle of Marathon [2]. This was a battle between the Persians and the Greeks that the Greeks somehow won. Had they lost it would've changed the entire history of Europe given how important Greek culture was to everyone from the Romans on. Bear in mind when this happened, Rome was a small regional power at best.
He talks about the psychology of ancient warfare. One thing he notes is that the closer someone is to someone, the harder it is for them to (psychologically) kill them. From a gun at a distance is completely different to hand-to-hand combat.
At this time, the Greeks fought with spears that were very broad. Stab someone in the guts with one of those and their insides would literally spill out to the point where the likes of Herodotus described the ground at Marathon as being soaked red in blood.
Likewise, ancient culture and justice must be almost incomprehensible to us. Fun fact: the origin of the word "decimate". When a province rebelled against Roman Rule and Rome would crush them, insurrection was punished particularly harshly. People would be put in groups of 10 (hence DECImate) where each group was responsible for choosing which of those 10 would die and for killing that person.
How did people cope with these things? How would PTSD fit into this world?
EDIT: the way some downvote on HN makes me sad.
[1]: https://www.dancarlin.com/
[2]: https://en.wikipedia.org/wiki/Battle_of_Marathon