The size of the Roman Empire was determined by the geophysical reality of military coordination across three continents, the ability to control the military class, and the cost of maintaining a large army.

The size of the Roman Empire was determined by the geophysical reality of military coordination across three continents, the ability to control the military class, and the cost of maintaining a large army. At its peak, Roman military rule created lasting peace, a boon shared by subjects and citizens. In the heart of the empire, one could leave the pain of war far behind. "Many people in the provinces don't know where their garrisons are; all are more happy to pay taxes to you than others to collect taxes from others." "These cities shine with brilliance and elegance, and the whole land is decorated like amusement gardens; the smoke rising from the fields, from the signal platforms of friends and enemies, away from land and sea."