As a leopard can jump fifteen feet and a tiger can jump twenty, the podium wall was obviously not enough to protect the spectators. However, elephant tusks about five feet long were fixed to the edge of the podium and nets strung along them in such a way that they overhung the arena. In addition, a bronze bar ran along the top of the wall that turned on a pivot so if an animal did jump high enough to grab the bar, it would turn and drop him back into the arena. There was also a moat as in the Circus Maximus. The moat was mainly to break the force of an elephant charge. Without such protection, elephants could easily reach the nobility in the podium—as was discovered when Pompey first exhibited elephants in the Circus Maximus in 55 b.c. before Julius Caesar had the moat dug. Iron gratings had been put up for additional protection, but the elephants ripped these down and only fast footwork on the part of the emperor and his friends saved their lives.
These precautions might seem enough, but most authorities believe that there was also an inner wall of heavy wooden planks running around the arena about ten feet from the podium wall and that the moat lay between this inner barrier and the central part of the arena. There are several reasons for believing this inner wall existed. The Colosseum was so vast that there must have been some way of keeping the animals out of the middle of the arena and away from the podium wall—otherwise the people in the two upper tiers of seats couldn't have seen them because the edge of the podium would have cut off the view. The natural instinct of a wild animal turned loose in a brightly lighted arena full of shouting, yelling people is to hug the wall, and scattered references by Roman writers show that the animals in the Colosseum often did just that. They were driven away from the wall by arena slaves using hot irons or burning straw. but there are no openings in the podium wall through which the slaves could have reached the animals. Also, there are many references to the elaborate scenic effects which acted as backdrops for the shows; the animals issuing from artificial caves, gladiators fighting before a painting representing ancient Carthage, and so on. It is hard to see how this scenery could have been erected and taken down if it were hung on the podium wall, especially as the changes often had to be made while the arena was full of wild animals and certainly the slaves were not allowed on the podium itself among the noble onlookers.
All these facts suggest that there must have been an inner wall, probably made of heavy planks fastened to poles set into the floor of the arena. The elephant tusks carrying the overhanging nets may have been fastened to these poles rather than to the podium wall itself. This inner wall could be painted, or have painted canvases hung on it, representing any scene desired. It may not always have been a board fence, but composed of artificial rocks made of lathes and plaster, tree trunks to represent a forest or any other material that the stage designers of the Colosseum decided to use.
The slaves who changed the scenery could operate between the podium wall and this inner barrier. The barrier must have joined the podium wall at the Gate of Life and the Gate of Death. The overhanging nets couldn't be used at these two places, but Calpurnius says that revolving ivory wheels were set into the podium wall at these points to keep the animals from climbing it
There must have been at least a circle of tall masts in the arena itself, for the great awning which covered the top of the Colosseum to protect the audience from sun and rain had to be supported in the centre by some means. We know that around the top of the Colosseum ran a circle of 240 masts (the sockets where they stood can still be seen) and these masts held the edge of the awning. However, unless the Romans had some very ingenious method for keeping the awning taut, there must have been masts coming up from the arena to take the weight of the great mass in the centre. There may even have been wooden catwalks running across the top of the Colosseum under this awning, as on a modern Hollywood sound stage, for the ancient writers talk of naked little boys with wings tied to them to represent cupids being swung back and forth across the arena by invisible wires as though they were flying. Often large animals, in one case a bull, were carried up to the awning (which was painted to represent the sky) by invisible wires to illustrate some mythological incident. To make such stunts as this possible, there must have been platforms at the top of the building equipped with blocks and tackles as well as space for crews of highly trained stagehands. Yet no matter how complicated were the mechanical miracles that these men had to produce, there was seldom a hitch in the performance. If there was, the stagehands were thrown into the arena to be eaten by wild beasts or killed by gladiators.
The games, were worked on a very tight schedule and something had to be going on every minute or the crowd became restless. Anyone who had ever had any connection with a modern circus knows what a tremendous problem it is to get the various acts, especially the animal acts, on and off on time. The Romans were working with wild animals and~ condemned criminals so their problem was incredibly complicated. They were also operating on a gigantic scale— the games often ran for a couple of months, and sometimes five thousand animals were in the arena at the same time.
Getting such a huge number of animals out of their cages and into the arena must have been a fantastic job.
We have a pretty good idea how the Romans did it from studying the honeycomb of passages under the arena. The Romans used at least four systems. The cages could be dragged up to the arena on a series of ramps and then put into niches under the podium wall. At a given signal, all the doors were opened simultaneously and at the same time slaves dropped burning straw into the backs of the cages through slots in the top specially provided for this purpose. If there was an inner wall, the animals must have reached it by runways as lions enter the big cage in a modern circus. Or perhaps the cages were only kept in the podium niches so they'd be ready when the time came. As soon as the previous act—chariot racing, gladiators or whatever—was finished, the cages were quickly pulled from their niches in the podium wall, dragged to openings in the inner barrier, and opened there.
Another method, probably used with less dangerous animals than the big cats, was to turn them loose in a passageway leading to the arena and then force them on with a movable wooden barrier that just fitted across the passage. There were catches on the sides of the barrier that fitted into holes on the walls so the barrier couldn't be pushed back. These holes can still be seen.
Still another method was to put the animals into an elevator and take them directly up to the floor of the arena. There were a number of these elevators placed at various spots in the arena like trapdoors on a modern stage. The elevator went down into a deep well, the animals were driven onto it, and then the platform was hoisted to arena level by pulleys. In some cases "breakaway" cages were used that would fall to pieces when certain pins were released. These cages were carried out into the arena, the pins jerked clear, and the animals left exposed as the sides of the cages fell to the ground. The Romans also had cages that operated on the same principle as the chutes used in rodeos; that is, the two sides were hinged so that they could be swung back parallel with the rear, leaving the animal completely exposed. All these devices were necessary as it is almost impossible to induce a frightened animal to leave its cage under normal conditions.