ROMAN ARCHITECTURE. 159 their size and proportion striking features of the Roman landscape. Throughout the Empire remains are to be seen showing the importance put by the Romans upon an adequate water supply to their cities. Rome had to be especially well supplied owing to the inferiority of the local service and the large quantity required for the reservoirs, great thermae and public fountains, to say nothing of the domestic supply for its large population. In any views of the Campagna near Rome, the ruined aqueducts are striking features, and in approaching the Eternal City in the days of its glory, these enormous arched waterways must have impressed the beholder. Vitruvius (Book VIII., chapter vii.) gives interesting information on the subject, which is added to from other sources by Middleton. The Romans were acquainted with the simple hydraulic law that water will rise to its own level in pipes, and the upper rooms of their houses were supplied by " rising mains " in the same way as modern buildings. Owing, however, to the fact that pipes had then to be made of weak and costly lead or bronze (cheap and strong cast-iron pipes not being in use), it was found to be more economical by the use of slave labour to construct aqueducts of stone, or concrete faced with brick, having almost level water channels, above or below ground (Vitruvius recommends a fall of 6 inches to every 100 feet), on immense arches above ground, a system which even in modern times has been followed in the Croton Aqueduct which supplies New York City. The principle of all the examples is similar. A smooth channel (spcciis) lined with a hard cement, is carried on arches, often in several tiers and sometimes of immense height (say 100 feet), con- veying the water from the high ground, across valleys, to the city reservoirs. Many of them follow a circuitous course in order to prevent the slope of the channel being too steep when the source of the water was high above the required level of distribu- tion in Rome. In the time of Augustus Csesar there were nine of these aqueducts supplying Rome with water. The Aqua Marcia (b.c. 144) and the Aqua Claudia (a. d. 38) still supply water to Rome. The " Anio Novus" (a.d. 38), sixty-two miles in length, entered the city on arches above those of the Aqua Claudia. The Pont-du-Gard, near Nlmes, in France (b.c. 19; (Nos. 60 A, B and bi), is the finest existing example. It forms part of an aqueduct twenty five miles long, bringing water from the neigh- bourhood of Uzes. It is about goo feet long, and is formed of three tiers of arches crossing a valley 180 feet above the River Gard. On the two lower tiers the central arch is the widest, and the others vary in width. On the uppermost tier there are thirty- five arches having 14 feet span, supporting the water-channel. The masonry is laid dry without mortar and, as will be seen on
