I cannot enter so fully into the topography of Rome as to show you how the streets of Rome were continued throughout Italy and the whole Roman empire. But, as architectural structures, the Roman high-roads are the most magnificent remains of antiquity. They consist of polished polygons of basalt: the foundation was formed of large stones, more than a cubit deep; over them was laid a stratum of mortar made of lime and puzzolano. Upon this a kind of excellent bricks were broken in large pieces, and laid in strata, over which again a cement was poured, which completely hardened into stone. Upon this substratum the blocks of basalt were placed, the lower surface of which was cut perfectly smooth. The polygons were very large, but different in circumference; they are so well fitted together, that in many parts the point of a pen-knife cannot be pressed between them; they were cut with great care, and must have been polished in a peculiar manner. A line is seen between two stones, but there is no interstice. Even if accidentally the water penetrated from above, the lower part was perfectly waterproof. It is well known that roads are mainly injured by water. Whoever has seen those ancient roads, despises the wretched structures of modern times; but if we were to build them now in the same manner, we should be obliged to sacrifice their external beauty and cover them with sand, because horses shod with iron would not be able to run on the surface, which is as smooth as a mirror. The horses of the ancients were not shod, and mules had either a kind of wooden shoes or soles of matting. Near and at Tivoli large parts of such roads exist in a state of preservation so perfect, as if they had been made only a year ago; but no vehicles now go over them. In comparison with ourselves, the ancients used carriages very rarely, and burdens were mostly carried by mules. On each side of the road there was a pavement for foot-passengers, and at intervals stones were set up, to enable men to get upon their horses, as stirrups were unknown. In regard to the interior of Rome, it is erroneous to speak only of hills, for in later times they constituted only the smallest part of the city; a great portion being situated in valleys and another in plains. But I will first speak of the hills.