As combats of wild beasts formed a chief part of the amusements, they were secured in dens around the arena or stage, which was strongly encircled by a canal, to guard the spectators against their attacks. These precautions, however, were not always sufficient, and instances occurred in which the animals sprung across the barrier. This huge pile was commenced by Vespasian, and was reared with a portion of the materials of Nero's golden palace: its form was oval, and it is supposed to have contained upwards of eighty thousand persons. A large part of this vast edifice still remains. Theatres, in the first ages of the commonwealth, were only temporary, and composed of wood. Of these, the most celebrated was that of Marcus Scaurus--the scenes of which were divided into three partitions, one above another, the first consisting of one hundred and twenty pillars of marble; the next, of the like number of pillars, curiously wrought in glass. The top of all had the same number of pillars adorned with gilded tablets. Between the pillars were set three thousand statues and images of brass. The _cavca_ would hold eighty thousand men. Pompey the great was the first who undertook the raising of a fixed theatre, which he built nobly of square stone. Some of the remains of this theatre are still to be seen at Rome. The _circi_ were places set apart for the celebration of several sorts of games:--they were generally oblong or almost in the shape of a bow, having a wall quite round, with ranges of seats for the convenience of spectators. At the entrance of the circus stood the _carceres_ or lists, whence they started, and just by them, one of the _metæ_ or marks--the other standing at the farther end to conclude the race. The most remarkable, was the _circus maximus_, built by Tarquinius Priscus:--the length of it was four _stadia_, or furlongs, the breadth the same number of acres, with a trench of ten feet deep, and as many broad, to receive the water, and seats enough for one hundred fifty thousand men. It was extremely beautiful and adorned by succeeding princes, and enlarged to such a prodigious extent as to be able to contain in their proper seats two hundred and sixty thousand spectators. The _naumachiæ_ or places for the shows of sea-engagements are no where particularly described; but we may suppose them similar to the _circi_ and amphitheatres. The _stadia_ were places in the form of _circi_, for the running of men and horses. A beautiful one was built by Domitian. The _xysti_ were places constructed like porticos, in which the wrestlers exercised.