The most remarkable of the nine aqueducts were the Anio Vetus, the Aqua Marcia, the Aqua Claudia, and the Anio Novus. The Anio Vetus brought a supply from the river Anio, a distance of forty miles. It was built B. C. 273, and consisted of a stone water-course, the channel of which was coated with cement. A still longer one was the Aqua Marcia, extending along a distance of fifty-four miles, six and a half miles being above ground, and chiefly supported on arches. So lofty was the level of the terminal reservoir, that the highest parts of the Capitoline Mount could be supplied from it. This aqueduct united toward its termination with two others, in the same pile of masonry, so as to form one range of building, in which the three water-courses occupied different levels, one above the other, and finally discharged their streams into the same reservoir. At the same period that this aqueduct was constructed, 700 wells, 150 springs, and 130 subordinate reservoirs, were added to the former sources of supply. The Marcian Aqueduct was remarkable for the vastness and solidity of its proportions and construction. Augustus caused an aqueduct to be built specially for the purpose of supplying the vast basin in which he exhibited sham naval fights to the citizens: but the Anio Novus, one of two new aqueducts built by the Emperor Claudius, was the most striking of all in its architectural effect. For six miles before its entrance into the city the water flowed along a channel supported by arches, some of which reached the height of 109 feet, and constituted a range of great beauty. When an aqueduct was to be constructed, the first step consisted in forming a large basin at the source of the supply. In this the liquid rested to deposit its impurities, and for a similar purpose the channel was expanded into other reservoirs at various intervals along its course. The channel in which the water flowed was formed of stone or brick, covered with a layer of cement. The slope of the water-course, according to Pliny, was only one quarter of an inch in every hundred feet, but Vitruvius makes it six inches in the same distance. It probably varied with circumstances. An arched covering excluded the sun, and vent-holes in the sides or top provided for a free circulation of air. From the castella or reservoirs lying along the course of the channel, adjacent lands were sometimes irrigated. From the terminal reservoir the water was conveyed to its various destinations through pipes of metal or earthenware. These terminal reservoirs were works of great size and solidity. One such at Cuma is 200 feet long by 130 wide, and is covered in by a vaulted roof resting on four rows of pillars. At Rome there were 247 subordinate basins, in which the water from the terminal reservoirs of the various aqueducts was collected, previously to passing to the baths and houses. A staff of officers and a body of laborers were specially provided to keep the aqueducts in repair.