One of the first objects of Augustus, after he had obtained the empire, was to secure the command of the sea:  he made use of the ships which he had captured from Anthony to keep the people of Gaul in subjection; and he cleared the Mediterranean of the pirates which infested it and obstructed commerce.  He formed two fleets, one at Ravenna, and the other at Misenum; the former to command the eastern, the latter the western division of the Mediterranean:  each of these had its own proper commanders, and to each was attached a body of several thousand mariners.  Ravenna, situated on the Adriatic, about ten or twelve miles from the most southern of the seven mouths of the Po, was not a place of much consequence till the age of Augustus:  that emperor, observing its advantages, formed at the distance of about three miles from the old town and nearer the sea, a capacious harbour, capable of containing 250 ships of war.  The establishment was on a large and complete scale, consisting of arsenals, magazines, barracks, and houses for the ship-carpenters, &c.:  the principal canal, which was also formed by Augustus, and took its name from him, carried the waters of the river through the middle of Ravenna to the entrance of the harbour.  The city was rendered still stronger by art than nature had formed it.  As early as the fifth or sixth centuries of the Christian era the port was converted, by the retreat of the sea, into dry ground, and a grove of pines grew where the Roman fleet had anchored.

Besides the principal ports of Ravenna and Misenum, Augustus stationed a very considerable force at Frejus, on the coast of Provence, forty ships in the Euxine, with 3000 soldiers; a fleet to preserve the communication between Gaul and Britain, another near Alexandria, and a great number of smaller vessels on the Rhine and the Danube.  As soon as the Romans had constant and regular fleets, instead of the legionary soldiers, who used to fight at sea as well as at land, a separate band of soldiers were raised for the sea service, who were called Classiarii; but this service was reckoned less honourable than that of the legionary soldiers.

The period at which we are arrived seems a proper one to take a general view of the commerce of the Roman empire; though, in order to render this view more complete, it will be necessary in many instances to anticipate the transactions posterior to the reign of Augustus.  We shall, therefore, in the first place, give a statement of the extent of the Roman empire when it had reached its utmost limits; secondly, an account of its roads and communications by land; and, lastly, an abstract of the principal imports into it, and the laws and finances, so far as they respect its commerce.