That phrase Jesus tells his disciples when being consulted for tax advice—"Render unto Caesar what is Caesar’s"?

That wasn’t just about what to do with your material goods, it was also a religious question. 

Because the Romans had figured out and damn near perfected something the many empires before theirs weren’t nearly as successful at: how to ensure obeisance from your conquered subjects.

And while the guarantee of material gain for the people you crushed in war goes a long way, sooner or later they start wanting more. After all, you did kill their fathers, rape their mothers and pillage their homes.

It doesn’t matter if you then give them aqueducts, deep down they still want to see you die. The physical is easy, the spiritual and mental are much harder to conquer.

Unless...