HISTORY OF ENGINEERING.
Book I.
184
Fig. 214.
In one part of the aqueduct was a double channel, formed by a division wall, which wasconsidered serviceable in case of a repair being required.
The quantity of water which flowed to Metz was calculated at upwards of a thousandcubic feet per minute.
Aqueduct of Evora in Portugal , in the province of Alemtejp, was constructed, as well asa temple to Diana, by Sertorius . This town, the third of importance in the kingdom,abounded with Roman remains. The aqueduct is in good preservation, the arches are 13feet 6 inches in span ; the piers 9 feet in breadth, and 4 feet 6 inches in thickness. In someinstances additional strength is given by buttresses. All the work is executed in stone, withthe exception of the arches, which are in tile or brick. The castellum, of fine proportions,remains very perfect; its form is circular, 12 feet 6 inches in diameter; on the exterior areeight Ionic columns, between which are as many niches, with hemispherical heads, throughone of which is an entry to the interior. Over this order is another formed of pilasters,and the chamber was covered by an hemispherical dome.
The Aqueduct at Carthage. Its ruins may be traced for. a distance of fifty miles, at thevillage of Arriana, near Tunis ; one range of arches is entire, 70feet high, with piers 16feet square, built of a hard durable limestone, and excellent mortar. Many of the cisternsfor the reception of the water, built of rubble and cement, remain, though converted intodwellings and stables. Other smaller cisterns, 93 feet in length, 20 in width, and 27 inheight, to the vault, are met with. Temples were erected over the fountains which suppliedthis aqueduct; the conduit for water was 6 feet in height, and 4 in width, gathered in atthe top like a pyramid, and lined internally with a beautiful cement, in high preservation.This aqueduct passed by a tunnel through the hill, and at every 180 feet perpendicularshafts, 4 feet in diameter, were formed of courses of squared stone, which were carriedup 4 feet above the surface of the ground; these shafts were used for drawing up the soil,and afterwards left for ventilation.
Near Udena is another aqueduct, built by the Carthaginians; a thousand arches of beau-tiful masonry remain, which are upwards of 100 feet in height; some writers say this wasthe work of the Romans after they had subjugated the country.
The Aqueduct of Segovia , built by Trajan , of squared stone, laid without mortar, extendsupwards of 2220 feet across a valley ; in many places it is nearly 100 feet in height.