In modern times, we think of great navies patrolling the oceans of the world. The British Empire, for example, owes the advent of its naval superiority to its victory over the Spanish Armada and the subsequent focus on providing protection for its trading partners and colonies. In Roman times, the naval landscape was principally the Mediterranean Sea, or as the Romans liked to call it, Mare Nostrum.
As I have discussed in other posts, the Romans came late to the game of sea trade and naval power following the successes of the Phoenicians, Greeks, and Carthaginians. They had no navy until the first Punic War (264 B.C.) when it became an important instrument for the capture of Sicily. By the time the empire began, naval power was a critical element of Roman strategy.