Rome is the connecting link between antiquity and mediævalism. The great empire sprang from a single city, whose power and dominion grew until it comprised every civilized nation living upon the three continents then known. Under the emperors, the Roman empire extended from the Atlantic to the Euphrates, a distance of more than three thousand miles, and from the Danube and the English Channel to the cataracts of the Nile and the Desert of Sahara. Its population was from eighty to one hundred and twenty millions. The empire was covered with a net-work of excellent roads, which stimulated, together with the safety and peace which followed the civil wars, traffic and intercourse between the different regions united under the imperial government. More than 50,000 miles of solidly constructed highways connected the various provinces of this vast realm. There was one great chain of communication of 4,080 Roman miles in length from the Wall of Antoninus in the northwest to Rome, and thence to Jerusalem, a southeastern point of the empire. There were several thousand miles of road in Italy alone. Rome's highways were constructed for the purpose of facilitating military movements, but the benefits which commerce derived from them cannot easily be overestimated. These military roads were usually laid out in straight lines from one station to another. Natural obstacles were frequently passed by means of very extensive works, as excavations, bridges, and, in some instances, long tunnels. The resources of the Roman Empire were almost inexhaustible, and no public expenditures were larger than those made on account of the construction of new roads. The fact that many of these roads have borne the traffic of almost two thousand years without material injury is abundant proof of the unsurpassed solidity of their construction. The Roman engineers always secured a firm bottom, which was done, when necessary, by ramming the ground with small stones, or fragments of brick. Upon this foundation was placed a pavement of large stones, which were firmly set in cement. These stones were sometimes square, but more frequently irregular. They were, however, always accurately fitted to each other. Many varieties of stone were used, but the preference was given to basalt. Where large blocks could not be conveniently obtained, small stones of hard quality were sometimes cemented together with lime, forming a kind of concrete, of which masses extending to a depth of several feet are still in existence. The strength of the pavements is illustrated by the fact that the substrata of some have been so completely washed away by water, without disturbing the surface, that a man may creep under the road from side to side while carriages pass over the pavement as over a bridge. The roads were generally raised above the ordinary surface of the ground. They frequently had two wagon-tracks, which were separated by a raised