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 o…
This is incorrect. Decimation was a form of military discipline, not civilian, and it was _extremely_ rare for most of Rome's history. It was usually used for mass desertion. Thousands of people were executed for individual desertion during WW1, so you could argue that it's not THAT exotic a punishment.
The Roman Empire _did_ do various nasty things to rebellious provinces (Judea is particularly notable), but again, really nothing that we haven't seen in 20th century wars, unfortunately.