All these cities were connected with each other, and with the capital, by the public highways, which, issuing from the Forum of Rome, traversed Italy, pervaded the provinces, and were terminated only by the frontiers of the empire. If we carefully trace the distance from the wall of Antoninus to Rome, and from thence to Jerusalem, it will be found that the great chain of communication, from the north-west to the south-east point of the empire, was drawn out to the length of four thousand and eighty Roman miles. 85 The public roads were accurately divided by mile-stones, and ran in a direct line from one city to another, with very little respect for the obstacles either of nature or private property. Mountains were perforated, and bold arches thrown over the broadest and most rapid streams. 86 The middle part of the road was raised into a terrace which commanded the adjacent country, consisted of several strata of sand, gravel, and cement, and was paved with large stones, or, in some places near the capital, with granite. 87 Such was the solid construction of the Roman highways, whose firmness has not entirely yielded to the effort of fifteen centuries. They united the subjects of the most distant provinces by an easy and familiar intercourse; but their primary object had been to facilitate the marches of the legions; nor was any country considered as completely subdued, till it had been rendered, in all its parts, pervious to the arms and authority of the conqueror. The advantage of receiving the earliest intelligence, and of conveying their orders with celerity, induced the emperors to establish, throughout their extensive dominions, the regular institution of posts. 88 Houses were everywhere erected at the distance only of five or six miles; each of them was constantly provided with forty horses, and by the help of these relays, it was easy to travel a hundred miles in a day along the Roman roads. 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