[89] [891] The use of posts was allowed to those who claimed it by an Imperial mandate; but though originally intended for the public service, it was sometimes indulged to the business or conveniency of private citizens.

[90] Nor was the communication of the Roman empire less free and open by sea than it was by land.

The provinces surrounded and enclosed the Mediterranean: and Italy, in the shape of an immense promontory, advanced into the midst of that great lake.

The coasts of Italy are, in general, destitute of safe harbors; but human industry had corrected the deficiencies of nature; and the artificial port of Ostia, in particular, situate at the mouth of the Tyber, and formed by the emperor Claudius, was a useful monument of Roman greatness.

[91] From this port, which was only sixteen miles from the capital, a favorable breeze frequently carried vessels in seven days to the columns of Hercules, and in nine or ten, to Alexandria in Egypt.