Image: locations of Roman legions - Wikipedia
* The Romans were able to copy and adapt the weapons and methods of their opponents more effectively. Examples include weapons like the gladius and warship design.
* Roman organization was more flexible than those of many opponents. Over time, the legions effectively handled challenges ranging from cavalry, to guerrillas, to siege warfare.
* Roman discipline, organization and systemization sustained combat effectiveness over a longer period. These elements appear throughout the legion in training, logistics, field fortification etc.
* The Romans were more persistent and more willing to absorb and replace losses over time than their opponents. Wars with Carthage, the Parthians and barbarian forces illustrate this.
* Roman leadership was mixed, but over time it was often effective in securing Roman military success.
* The influence of Roman military and civic culture, as embodied particularly in the heavy infantry legion, gave the Roman military consistent motivation and cohesion.
Book of the Week: "The History of the Decline and Fall of the Roman Empire" by Edward Gibbon - The World 2 Come