Vitruvius gives rules for testing the water, and points out that water led through earthen pipes is more wholesome than water coming from leaden ones. He states that the "fall" of an aqueduct should be not less than 1 in 200. A circuit was often made to prevent the too rapid flow of the water, and intermediate reservoirs were constructed to avoid a shortage of water in the case of a broken main. Reservoirs were also used for irrigation. The water from the aqueduct was received at the walls of the city in a great reservoir called _castellum aquarum_, externally a beautiful building and internally a vast chamber lined with hard cement and covered with a vaulted roof supported on pillars. The water flowed thence into three smaller reservoirs, the middle one filled by the overflow of the two outer ones. The outer reservoirs supplied the public baths and private houses, while the middle one supplied the public ponds and fountains, so that, in the event of a shortage of water, the first supply to fail was the least important. The amount of water provided for private use could be checked, for purposes of revenue, by means of this arrangement. At first the aqueducts were not connected with private houses, but, later, private persons were allowed to buy the water which escaped from leaks in the aqueducts. Next, private connections were made with the public mains, and, finally, reservoirs were built at the expense of adjoining households, but these reservoirs, although built with private money, were considered part of the public property. Water rights were renewed with each change of occupant. The water-supply to a house was measured by the size of the pipe through which it passed at the in-flow and at the out-flow of the reservoir. The _curatores aquarum_ had very responsible duties. Under their orders, in the time of Trajan, were 460 slaves who were subdivided into various classes, each of which had its own particular duties to perform in connection with the maintenance and control of the water-supply. A supply of pure water and proper drainage are of first importance in sanitation, and it is evident that the Romans understood these matters well. DRAINAGE. The drains of Athens, built of brick and stone and provided with air-shafts, ran into a basin from which pipes carried the sewage beneath the surrounding plain which it helped to fertilize. The chief drain of Rome was the Cloaca Maxima, and there was a great network of smaller drains. The privy in private houses was usually situated near the kitchen, and a common drain from the kitchen and the privy discharged into the public cloaca. A pipe opened just above the floor of the closet to supply water for flushing. Ruins of very small rooms have been discovered in the Via Sacra of the Roman Forum, and it has puzzled archæologists to discover their use, but they are thought to have been sanitary closets. The sewers of Rome drained into the Tiber. DISPOSAL OF THE DEAD.