What advantages did controlling the Mediterranean Sea have for Rome's military and economic interests?
Controlling the Mediterranean Sea was not an option for Rome; it was a necessity, albeit one only grudgingly acknowledged. Vital trade routes both encircled and crossed the Mediterranean, and Rome's capacity for shipbuilding and navigation -- born of necessity given the threat from Carthage, which led to the Punic Wars -- enabled the Romans to confront maritime challenges before they could prove fatal. Roman command of this vast sea enabled it to extend its reach throughout the entire circumference of the water's coastline. To the extent that military and economic considerations occasionally intertwine, as they did regularly for the Romans and their need to secure the extensive lines-of-communication essential for maintaining control of distant territories and for facilitating trade with those far-flung provinces, control of the Mediterranean was absolutely essential. Additionally, and obviously, the Italian peninsula, known then as Italia, is, by definition, surrounded by the Mediterranean, and control of the maritime approaches was important for Rome's defense. All of this, however, was, as noted, only belatedly acknowledged by the Romans. Rome lacked the maritime tradition of other great civilizations despite its obvious proximity to the sea. Among its strengths, though, was its capacity to adapt, and it did so with respect to the need to defend itself against attacks from the sea.
Rome's interest in the Mediterranean tended to vary according to threats and challenges of a specific time. The empire was overwhelmingly concentrated on land and land routes were of primary importance to Rome, evident in its successful construction of its system of roads. Command of the sea was vital to confronting military threats, but most of Rome's economic activities were oriented in other directions, and the sea was exploited merely as a means of transporting goods quicker than some land routes offered.