To protect the people in the lower gallery from these wild beasts, a strong netting was provided (as has been mentioned); this was of gold wire, fixed in a wooden frame, and at the top was an ivory rod which turned round, so that if an animal should attempt to cling to it, he would necessarily fall back. This net was called _retia_, and at Puteoli or Pozzuoli it was either of gold, or gilt; and this was the case in the Colosseum also, and in other instances. Our authority for this is Calpurnius in his Eclogues[212]. The naval fights with the larger vessels were sometimes held in the Circus Maximus, which could be flooded to the depth required by stopping up at the lower end the stream that runs through it, which is in fact a branch of the small river Almo, but was in this part called the Euripus. This name was also given to the canals for the _naumachia_, as in the Colosseum. This must have been the case, because the Emperor Heliogabalus upon one occasion filled these canals with wine, which could not have been done in the Circus Maximus, where the Euripus was a natural running stream of water; but in the Colosseum a canal supplied with water from an aqueduct, which could be let in or drawn off at pleasure, might very well have been filled with wine during an abundant season, when in Rome the wine is sometimes worth less than the vessel that holds it, so that large quantities are frequently wasted for want of casks to put it in. In all wine-growing countries, the same thing occurs from time to time in superabundant seasons. It is true that these naval fights were called Circensian games, because they were sometimes held in a circus (as has been said), but the same name was given to them when they were held in the amphitheatre, as in this instance, by Lampridius[213]. Martial[214] distinguishes very clearly both the one and the other, and makes it evident that the _stagna_ of Nero were used for the _naumachia_ of the Cæsars. That the vaults under the arena were called _caveæ_, caves (or cavities), has been already mentioned, and is evident from many passages in classical and mediæval authors; as in Tertullian and in Prudentius[215], when describing the scenes that had taken place in the amphitheatre as the wicked rites in which the gladiators were killed on the arena, and the impious games in which the sad spectacles of funereal character were brought up from the caves, worthy only of the infernal Jupiter (whom the Christians call Satan). THE ARENA.