This vast amphitheatre is of an elliptical shape, which gives it great powers of resistance. According to the best and most recent measurement, it must be about one thousand one hundred and eighty eight feet in external circumference, the long axis being six hundred and twenty-eight, the short five hundred and forty, and the total height one hundred and sixty feet.[189] The whole is a vast mixed mass of enormous blocks of stone and bricks, (probably portions of the golden palace), metal and cement, which have become so hardened by time, as to be like solid rock. The exterior was entirely of calcareous tufa of Tivoli, called travertine, a fine hard and white stone. It presents a series of three ranges of open arcades, so airy and correct in their proportions, that the building does not appear so large as it really is. Each tier consisted of thirty arches; the columns between which, together with the entablatures, displaying different orders of architecture, the lowest being Doric, the second Ionic, and the third Corinthian, surmounted by an attic story, with Composite pilasters, and forty windows. The two upper tiers of arches, which have the remains of pedestals for statues in them, admitted light to the various ambulacra or corridors, which were quadrangular at the base, diminishing in number and size as they ascended, and terminating in a single passage at the top. The lowest tier of arches were the entrances, seventy-six of which were for the emperor, finely ornamented; one for the spectators, of various denominations; and one for the consuls, senators, &c.; and two for the gladiators, animals, &c. These entrances led to the various staircases by which the populace gained the different dormitories, and descended by narrow flights of steps, to the graduated ranges of seats. Altogether there were one hundred and sixty staircases: that is,—to the first floor, sixty-four; to the second, fifty-two; to the third, sixteen; to the fourth, twenty-four; and four to the extreme top, for the workmen. In the four ambulacra on the ground floor, were shops, taverns, stables, and rooms for refreshments, and places where perfumes were burned. There was also a fifth, or private passage, under the pulvinar, for the use of the emperor, which communicated subterraneously with the palace. In the tier above were twenty-two small vaulted chambers, called fornices, devoted to the sensual pleasures of the privileged classes.