[Sidenote: Its great roads and engineering,] Through the entire length of the empire two great military roads were built, one on the plateau, the other on the shore. The former, for nearly two thousand miles, crossed sierras covered with snow, was thrown over ravines, or went through tunnels in the rocks; it scaled the more difficult precipices by means of stairways. Where it was possible, it was carried over the mountain clefts by filling them with masonry, or, where that could not be done, suspension bridges were used, the cables being made of osiers or maguey fibres. Some of these cables are said to have been as thick as a man, and two hundred feet long. Where such bridges could not be thrown across, and a stream flowed in the bottom of the mountain valley, the passage was made by ferry-boats or rafts. As to the road itself, it was about twenty feet in width, faced with flags covered with bitumen, and had mile-stones. Our admiration at this splendid engineering is enhanced when we remember that it was accomplished without iron and gunpowder. The shore road was built on an embankment, with a clay parapet on each side, and shade trees. Where circumstances called for it, piles were used. [Sidenote: and expresses by couriers.] Every five miles there was a post-house. The public couriers, as in Mexico, could make, if necessary, two hundred miles a day. Of these roads Humboldt says that they were among the most useful and most stupendous executed by the hand of man. The reader need scarcely be told that there were no such triumphs of skill in Spain. From the circumstance that there were no swift animals, as the horse or dromedary, the width of these roads was sufficient, since they were necessarily used for foot passage alone. [Sidenote: Cuzco--the military centre.] In Cuzco, the metropolis, was the imperial residence of the Inca and the Temple of the Sun. It contained edifices which excited the amazement of the Spanish adventurers themselves--streets, squares, bridges, fortresses surrounded by turreted walls, subterranean galleries by which the garrison could reach important parts of the town. Indeed, the great roads we have spoken of might be regarded as portions of an immense system of military works spread all over the country, and having their centre at Cuzco.