Roman strength came from logistics and standardisation

The Roman legions are presented as effective because logistics, standardized equipment, discipline, and engineering let them sustain repeated campaigns. Roman armies could still be beaten in Germany, the Sahara, the Carpathians, Persia, and Armenia. Rome's advantage was the ability to return with another well-equipped force and keep it in the field for months. That persistence depended on builders and engineers as much as battlefield skill. The empire could also abandon a frontier when the tax return no longer justified the cost.