118

HISTORY OF ENGINEERING.

Book I.

these latter posts in their places. Under the mortice holes are others, 8 inches square, and2 feet in depth, made in the upper step of the attic to receive the second posts. The twoposts were afterwards securely braced.

Over the centre of the arenawas an oval covering, perma-nently fixed, which in theColiseum was ornamentedwith an immense goldeneagle. Round the edge ofthis oval covering was at-tached a large cable. 120 pairof cords, of equal length,stretched from the masts onthe exterior to this cable,were worked by pulleys ; thusforming as many compart-ments. Each pair of cordswas furnished with rings, towhich the covering was at-tached, so that it could bedrawn backwards and for-wards at pleasure. Thewhole of these were calledthe vela or velaria, and eachsingle compartment velarium.

The distance between theropes on which the velariumran was greater towards theattic than at the centre; con-sequently, to make the vela-rium run freely on its rings,it was necessary that it shouldbe of an equal width through-out : when spread, towardsthe attic it was stretched,whilst towards the centre itsagged, and formed as it werea fold. To prevent the sunpassing through the openingthus made by the sagging, aninternal hanging was attachedaround the fixed permanentoval.

Fig. 131.

POSTS OF TTTE VELA.

The weight of the vela was sufficient to make it drop considerably in the middle, what-ever caution was used in tightening the ropes: another inconvenience to be guardedagainst was, the action of the wind upon it. At the back of the podium wall are remain-ing many holes, which contained iron rings, run with lead, supposed to have been usedto secure the blocks, through which passed perpendicular ropes, which being kept tightwould obviate this inconvenience.

Amphitheatre at Verona. The longest axis of the ellipsis is 495 feet; the shortest, 396feet. That of the arena within the podium is 240 feet, and the shortest diameter 141 feet.The total circumference of the exterior wall is 1419 feet; the height which remains is about88 feet, though originally it is said to have been upwards of 130 feet.

There are forty-five ranges of seats or steps remaining, exclusive of the first, and it wascalculated that 22,000 persons could have been accommodated within the walls. The outerwall is nearly demolished : it had three orders, and an attic built of coloured and whitemarble: the three lower had arches separated by pilasters. The mouldings of the upperstory, as well as the capitals and cornices of the other two, are of white marble. All theseats are of red marble. The stones used in the construction are of large dimensions, and passthrough the entire thickness of the wall; but the courses vary in height. On each storywere seventy-two arches, and each had its number engraved upon it. The staircases are wellcontrived, and in some degree resemble those of the Coliseum. There were in all sixty-sixentries, including the two great gates: six led into the arena; twelve straight passagesconducted to the seats over the podium, and each had five steps.

The wedges or cunei above were entered from the outer portico, by eight single stair-cases and four double ones. The fourth round had sixteen vomitories or openings, and wasascended by eight smaller staircases.