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HISTORY OF ENGINEERING.
Book I.
The division walls, which radiate from the third to the two outer corridors, have each fourdistinct piers of travertine stone, with spaces between filled with pepperino, the horizontaljoints of which do not always correspond. The walls between the third and fourth cor-ridors arc faced with tiles in regular courses; the outer pier is alone of travertine, and formsa break.
The vault of the fourth corridor is entirely destroyed; the marble pavement remains,5 inches thick, which seems to indicate that this was the approach to the podium, wherethe emperor and persons of rank were seated.
The rain which fell upon the several seats and the arena, and the water which flowedthrough urinals, and other arrangements made for the convenience of the multitudeassembled within the walls, drained into wide and spacious sewers, which were conductedinto the Cloaca Maxima . A large drain in the second corridor, 30 inches wide, receivedthe water, brought down by perpendicular pipes worked in the solid masonry, or placed inindents, lined with tile. The drain of the third corridor, 17 inches wide, and 3 feet indepth, is lined carefully with tile and coated with a fine cement. On the outer side of thethird corridor, a similar drain, with a fall towards the last described, caught all the waterbrought by the several branches from the arena.
The total area of this building has been stated to be about 249,840 feet; that of thearena, within the present podium wall, 40,575 superficial feet: consequently, the area occu-pied by the walls, piers, and corridors, will be the difference of these two quantities, whichwill be found to be 209,229 feet.
The true points of support are the following :—
80 outer piers, the area of which is
-
-
- = 5,360 ft.
80 second piers, the area of which is
-
-
- = 3,600
80 third piers, the area of which is
-
-
- = 2,640
80 division walls to the third corridor -
-
-
- = 14,400
80 division walls to the fourth corridor
-
-
- = 6,640
80 portions of the arena wall -
- = 9,200
41,840
The points of support are, in area, 41,840 feet, about one-fifth of the mass, or one-sixth ofthe total area of the entire amphitheatre, which is about the proportions that exist betweenthe total area and the points of support in St. Paul’s, at London .
The 80 piers and division walls are not set out very exactly ; they diminish in thicknessas they radiate to the four centres of the ellipsis.
Exterior elevation , consists of 4 stories of different orders formed of travertine stone. Theheight of the lower, or Doric , including its attic above, is 40 feet 7 inches, which is levelwith the pavement of the first story.
The height of the Ionic order and its attic, level with the pavement of the second story,is 38 feet 7 inches.
The height of the Corinthian order and its attic, nearly corresponding in level with thepavement of the upper internal corridor, is 40 feet.
The height of the upper wall, with the pilasters and its entablature, is 38 feet 4 inches.
The total height of the present wall is, as stated, 157 feet 6 inches.
The openings of the arches average 14 feet 4 inches, which is the height up to the top ofthe impost moulding, on which the semicircular arches rest.
The upper order, above the three ranges of corridors, has its cornice perforated for theinsertion of wooden masts, which supported the velarium; the total number were 240.Tlie interior portion of this wall is faced with tiles in regular courses, behind which, placedin indents, and well bedded in cement, are circular earthen pipes, that conveyed the waterfrom the wooden platform above to the drains below.
The piers are all formed of travertine stone in large blocks, many extending the wholedepth of the pier, which is 8 feet 8 inches ; the joints are well worked, and each stonesecurely cramped with metal, all of which, that could be removed, have been taken away.Each of the arches is formed of 11 voussoirs; the key-stone, as well as many of the others,extending through the whole depth of the wall. These voussoirs have on their sides mor-tices and tenons, which prevent their sliding, also iron cramps.
The Sections through the building exhibit its construction most perfectly. The back faceof the outer piers and wall above is perpendicular, the outer face retreating on eachstory. At the top it is 6 feet 9 inches in thickness ; at the Corinthian story, 6 feet 3 ; at theIonic, 8 feet 5 ; and at the lower, 8 feet 9 inches.
The width of the outer corridor in the clear is 17 feet, that of the second 14 feet 6 inches,that of the third 14 feet 6 also, and the fourth corridor 11 feet 6 inches.
The main piers are all of travertine stone; the division walls between the third and fourthcorridor, and those between the second and third on the first story, are faced with tiles filled inwith rubble work. The division walls between the second and third corridors have four piers in