1 IS
HISTORY OF ENGINEERING.
Book I.
formed the elliptical boundary of the amphitheatre. Their openings, with the exceptionof‘hose to the north, the east, and west, were all 12 feet 5 inches ; the other three 13 feet2 inches. The width of the external piers, 8 feet, the pilaster of which occupies 3 feet,and the faces on each side 2 feet 6 inches. The exterior has two orders surmounted byan attic ; the lowest without bases. The pilasters are in height 26 feet 3 inches, from thezoile to the top of the capital.
The second story, comprising pedestal, column, and entablature, is in height 29 feet 6inches ; the pedestal, 3 feet 6 inches ; the column, 20 feet 6 inches ; and entablature, 5 feet6 inches. The column projects two-thirds of its diameter, and at the base is 2 feet 7 inchesin diameter.
The height of the attic is 6 feet, and its face is fair with that of the column below:two strong stone corbels, pierced with circular holes, between the pedestals, supportedth» masts that received the cords of the vela or covering. There are thirty-five rangesof steps or seats, besides those which divided the whole into precincts. There arefour precincts, each having its separate staircases and vomitories. The lowest precinct,nearest the arena, reserved for the principal inhabitants, was formed to receive four seatsonly, each 1 foot 8 inches in height, and 2 feet 7 inches in width ; to protect the lowestof these seats, towards the arena, a podium or wall of one stone, 6 feet 6 inches in height,and 3 feet 3 inches, was built up.
The second precinct was separated from the one mentioned by a wall 3 feet 4 inches inheight; this consisted of eleven scats, and forty-eight vomitories, sixteen of which had theirentrance from the interior gallery of the ground floor, and thirty-two from the gallery ofthe entresol.
The third precinct, with ten rows of seats, was separated from the second by a step, in asimilar manner to the others. These were approached by thirty vomitories out of the galleryof the first story.
The fourth or upper precinct had ten seats, the last of which rested on the attic wall.Tney were arrived at by thirty vomitories whose entrances corresponded with the galleryof the second story.
The Staircases were numerous: twenty-eight conducted from the external gallery ofthe ground floor to the gallery of the entresol; a like number from thence to the firststory; thirty-two led from the gallery of the ground floor to the vomitories of the firstar.d second precinct. A similar number from the gallery of the entresol to the vomitoriesof the second precinct. Thirty others from the gallery of the first story communicated,first, to the thirty vomitories of the third precinct, and then to the double staircases, whichled to the second story, where the thirty vomitories of the fourth precinct were placed.Xnese last were contrived in the head of the vault of the gallery of the first story, andreceived their light from small openings pierced on each side of the capitals of the columnson the lower story.
The five several galleries held the spectators during the intervals of the exhibition orviolent storms: in a few moments the whole amphitheatre might, by means of the 130vomitories, have been cleared; and in a small space of time the spectators could, withoutconfusion, have again taken their seats.
The amphitheatre has been calculated to contain 23,362 spectators, each person occupyingonly fifteen inches superficial. The total length of the steps or seats is 30,660 feet; butsome allowance must be made for the loss by vomitories, &c.
For carrying off* the superfluous waters, which might collect in such vast edifices, themost ingenious contrivances were thought of and introduced at the very commencement ofthe work, and so admirably arranged as not to weaken the walls or piers which contain them.Many of these conduits served the double purpose of urinals, and numerous are the pre-cautions taken to prevent their becoming offensive, and to provide for their proper andthorough cleansing. The Roman engineers have taught constructors a lesson which hasnot been sufficiently appreciated nor imitated in the public buildings of modern times, wherevast numbers remain for many successive hours. By a careful study of the drainage of anamphitheatre, we shall be enabled to understand the attention paid to the setting out of thesewers of a city. The Coliseum and many large buildings retain all their pipes and drains,showing us how admirably this object was carried out; modern practice has not yet deviseda more perfect or effectual method.
Fifty-six drains, constructed within the thickness of the walls which supported the stair-cases of the ground floor, served for the rain water to pass off*, and for the convenience ofthe spectators placed in the third and fourth precincts. Their upper opening was on thelanding of the entresol, above the gallery of the first story ; half the openings of thesedrains were placed opposite the stairs which led to the gallery above, or that of the secondstory; the other half was enclosed, and formed into a recess, which concealed them from theview of those passing by. We presume the first were for the convenience of the men, andthe others for the women.
These drains were formed of cylindrical pipes 12 inches in diameter, hollowed out ofthe middle of large masses of freestone 20 inches in height, the beds of which were