Mention has frequently been made of the great central passage, which exists not only in the Colosseum, but in all other amphitheatres where substructures were made. This passage appears to have served for several useful purposes; there are traces of machines in it for lifting up some large object, not only in the Colosseum but also at Capua; and the things to be lifted up in all probability must have been the vessels for the naval fights. This central passage is mentioned or implied in several instances in the classical authors; it had the appearance of a gulf dividing the earth or _arena_ into two parts. Apuleius calls it _vorago terræ_ (a gulf of the earth); Martial, the _via media_, or middle way; and Petronius, _ruina terræ_, from the appearance of a swallowing-up the machines and the gladiators. The machines used for these public amusements were evidently numerous and important, and required a good deal of space to stow them away, more even than was afforded by the vaults and passages under the arena in the Colosseum. This is implied by the celebrated letter of Apollodorus, the architect, to the Emperor Hadrian, in which the architect told the Emperor that he _ought to have_ built the Temple of Roma at the south end of the Summa Sacra Via, and to have made room for this machinery of the amphitheatre in vaulted chambers under it (as before mentioned); _that he did not do so_ is evident, for the excavations of 1874 brought to light rude concrete walls of the time of the Republic, with a small aqueduct of the time of the Early Empire, made to carry water to the fountains at the corners of the _porticus_ above. The accounts which we have in classical authors, of the machinery employed in the amphitheatre, remind us very much of that used for a Christmas pantomime in one of the London theatres, and all these great shows were very much of the character of a pantomime. To begin at the top, the cords which carried the _velarium_, or awning, were strong enough for a rope-dancer, and were called by the name of _catadromus_; and we have an account in Suetonius, in the time of Nero, of an elephant being taught to walk upon these cords with a Roman cavalier on his back[200]. We also have an account of an actor trying to play the part of Icarus, and fly down from the top, falling dead at the feet of Nero, and sprinkling him with his blood[201].