The two great lofty walls of tufa are independent of the brick walls supporting the canals. The lifts, or _pegmata_ for the wild beasts, were placed in the outer passage between the two tufa walls, just under the edge of the _podium_[83]. On each side of the central passage are a series of small square closets for lifts, for men and dogs to ascend from the passages at the lowest level to the floor above, through the trap-doors. These continue visible for the whole length of the surface and central passage. The pavement of these passages is of brick in herring-bone fashion, such as was common in Rome during the first three centuries. Some persons have imagined that the walls are built upon this pavement, but if this is the case anywhere, of which there is no evidence, it would only be a part of the later repairs of the fifth or sixth century. There are some portions of a third wall of tufa parallel to the other two, and within them; this has been much damaged, and very little of it remains. In one place, near the south-west end, there is an arch in this tufa wall apparently much shaken by an earthquake, and consequently supported by two brick arches of Nero, one under it, the other abutting against it, like a flying buttress in a medieval church[84]. The long, thin bricks of the time of Nero are perfectly well known to all Roman archæologists, and are only met with in buildings of his time. Two other small square chambers, one on either side of the great central passage, also remain at the south end, with an arch of the brickwork of Nero on each side[85]. These chambers are enclosed in stone, so that half the thickness of the wall is of brick, the other half of travertine. This wall, therefore, affords conclusive evidence that there was a great theatre on this spot before the time of Vespasian, and that the tufa walls are _earlier_ than the time of Nero.