We are expressly told that Augustus had intended to build an amphitheatre here, but had not done so. We have no mention of Claudius having built one, we are therefore driven back to an earlier period (probably to the amphitheatre of Scaurus, in the time of Sylla) for the date of the tufa walls, with the grooves for lifts, or _pegmata_, in them, as has been mentioned. Outside of these great walls of tufa, and under the path in front of the _podium_, are a number of dens for lions, or other wild beasts of that size[86]. And in front of each is an opening large enough for the animal to pass through into a cage placed on a lift in the passage between the two tufa walls, and in each of these walls are vertical grooves cut in them for the lifts to work up and down; also deeper grooves, about a yard long, for the counter-weights[87]. Behind the place for each cage, in the passage, is a socket let into the pavement for a pivot to work in[88], apparently for a capstan or post to wind the cord upon to pull up the lifts and cages. These cages were of wood, and called _pegmata_. The word _pegma_ is used in different senses by Pliny, Martial, and others for a wooden box, cage, or framework; and the wild beasts were brought in such cages from the places where they were kept outside the walls, called _vivaria_. There were two _vivaria_, one on the southern side of the Prætorian Camp, of which there are some remains. The evidence for this is an inscription of the time of Gordianus III. (A.D. 241), which mentions a keeper of the _vivarium_[89] belonging to the sixth Cohort of the Prætorian and Urban[90] Guards. The other was on the southern side of the Sessorium, which was both a palace and a Prætorian Camp. The _podium_ was protected by nets[91]; and there were projecting bars for rollers, which turned round when touched, so that the claws of an animal could have no hold upon them: these are mentioned by Calpurnius. Seneca, in his Epistle (88) uses the word _pegma_ for “a wooden machine in the theatres,” which raised and lowered itself _imperceptibly_—evidently what we now call a lift—the machinery of which was not seen by the spectators. Wooden towers used on the stage in sham fights were also called _pegmata_[92]. The following account given by Seneca[93], who wrote about A.D. 20, of these machines, clearly applies to the Colosseum and the substructures under it. As that was before the time of the Flavian Emperors, it is probable that the wooden amphitheatre on this spot was in existence in his time, and that the tufa walls for the lifts now remaining were then standing and in use. He says—