By 284 A.D. Diocletian had removed the Praetorians from the palace and substituted his own version of a protection force. Finally, in 312, Constantine defeated a guard force supporting the usurper Maxentius, disbanded the guard, and demolished its camp in Rome.
So we have described the first of the causes of the fall of the Roman Empire according to Edward Gibbon. We’ve seen that when you create a private army to protect yourself from the public army, you lose the separation that maintains the mystique of the supreme leader. When the private army is able to observe the leader’s humanness close up, they may decide he’s no better than them.