Ducts of water according to Vitruvius, were of three kinds channels of masonry, leaden pipes, or tubes of fictile ware, according to the following rules when channels ;

are used they should be made as solid as possible, and the bed of the stream should have a descent not less than half a foot in 100 feet, and they should be arched over, that the sun's rays may not touch the water. When the water arrives at the city, a castellum or reservoir is built, and a triple emissary to receive the water is adjoined

to it. In the castellum are three pipes, equally disposed within the adjoining recep-

* Vide Maundrel, in Pinkerton's Collection 350. [Asia] vol. iv., p. 1.

t Vide Pococke, in Pinkerton's Collection [Asia] vol. iv., p. 439.

10 PRELIMINARY ESSAY.

tacle, so that when there is too much water, it may from the sides be discharged into the middle receptacle. In the middle channel are fixed the pipes leading to all the cisterns or fountains, in another, those to the baths, which pay to the people a yearly tribute, and in a

third, those to the private houses, if it be not wanted for public use, for they could not return it if they might have peculiar ducts from the spring head. This disposition is established, because by the tax on the water carried to private houses, the State keeps the

aqueduct in repair.

But, should mountains intervene between the city and the spring head, a subterranean passage is to be dug through the earth, having the declivity of one part in two hundred, and should the soil be either gravel or stone, a channel is to be cut into it, but walls are to be built to conduct the water through the earthy or sandy soils.