114

HISTORY OF ENGINEERING.

Book I.

received the rair. water and conducted it outside. A like number of drains is also contrivedabove the set-off of the staircases which led to the entresol and the first storv. Thegargouilles, pla?ed over each other, follow the direction of the stairs, then cross the wallswhich support them, pass behind the stone jambs of the porticoes and galleries of theentresols, then return under the landings and the stairs of the ground floor, and are at lastcollected in the receptacle connected with the great drains.

The draining so large a building occupied great consideration; the forethought displayedin these arrangements evinces great ingenuity and simplicity. The surface of the arenawas rather higher in the middle, and slopedgradually and uniformly towards the podium. ,

This form had the double advantage of di-viding the rain water, and preventing the in-jury which a collection in the centre wouldhave occasioned and of placing the spectacleon a plane, which by its form brought itnearer to the spectators. The convexity ofthe arena required the oval aqueduct to beplaced at a little distance from the walls ofthe podium, t> receive and conduct awayall the waters. It was consequently 7 feet6 inches distant from the wall of the po-dium, 3 feet 6 inches in width by 4 feet 9inches in depth. The walls are of moellonlaid in cement. Small channels very close to

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Fig. 129.

PLAN OP DRAIN.

each other are cut from the base of the podium, to conduct the water to the aqueduct.This aqueduct was covered with stone 8 inches thick, which rested on a bed of free-stone 6 inches high, forming a slightprojection on the internal face; theupper part is an inch and a halfbelow the base of the podium, bywhich means the sand that co-vered the arena extended also overthe flags which covered the aqueductsufficiently to prevent any injuryoccurring to the gladiators whenthey fell. These flags rest 8 inchesat each end on the bed of freestonewhich crowns the walls; they arealso attached by a dovetail half aninch in depth. The inclination orfall given to the bottom of theaqueduct is regular throughout.

Tire thickness of its side walls is18 inches. The outer part is backedagainst the concrete in which theaqueduct is entirely surrounded.

The wall on the side of the podiumis open opposite the two east andwest gates to receive the water of asecond inner aqueduct, which will behereafter described.

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Fig. 130. SECTION OF PIPES AND PLAN.

__ _ All the waters of the arena flowed into the inner aqueduct, and it

remains to show in what manner that which fell on the seats, in the vomitories and in thegalleries was carried through the opening of the great outer porticoes.

All the seats had an inclination of the sixteenth of an inch forwards, which facilitatedthe flowing of the water from the upper to the lower step, and from one to the other.The first precinct was defended in front by a parapet which rose 21 inches above thestep, so that the rain water which fell on the four rows of seats and the step of the firstprecinct, being stopped by the parapet, could not flow’ into the arena. The Romans mighteasily have pierced this parapet at the level of the step, and discharged the water of thisprecinct into the arena; but such an arrangement would have injured the ornamental effectof the podium.

The w’ater of the first precinct was therefore made to pass off by an opening at thebase of the first seat on the level of the step, to which, for this purpose, a slight fall wasmade towards the seat. Circular openings cut in a conical form, 4 inches in diameter,allowed the passage of the water from the first four rows of seats, and carried it behind theW’all of the podium, by a small conduit made in the stone step ; afterwards it was receivedat the foot of this wall into a small channel tw’o feet wide, which, traversing the lower part