The first use for all amphitheatres was only for fights of beasts: elephants, tigers, lions, panthers, bears, even crocodiles being introduced for the purpose of warring among themselves, and proving who was the victor in the struggle for supremacy. These sports gained in extent and luxury (so-called) according to the number and variety of beasts that could be obtained; and the rarer the animal exhibited in the arena, the greater the success of the entertainment. Thus when a hippopotamus and five crocodiles appeared on the scene, the triumph was well-nigh complete! Rhinoceroses and cameleopards were introduced by Julius Cæsar, and skilled hunters on the backs of elephants were set in array to combat against them. These sports were first held in the theatres or in the circuses, but the latter were intended really for horse and chariot races; the theatres for scenic representations. The difficulties both as to seeing and performing experienced in these buildings called for another kind of edifice, and led promptly to the formation of the arenas or amphitheatres of which such beautiful specimens remain to this day showing us even in their ruined or mutilated condition on what grand and colossal lines they were erected. The theatres of Greece and Rome served to give an idea on which the needed building should be erected. A semicircle of steps, spacious and uncovered, would serve to seat the audience, then in order to accommodate more spectators and fill in the space destined for the stage, another semicircle was added, leaving a vacuum in the middle suitable for games, sports, or fights. The first amphitheatres ever built were generally of wood, a material little adapted for this kind of building, and that on more than one occasion came to grief either from fire, or from the collapse of the entire structure. The latter event occurred during the reign of Tiberius Cæsar, when at Fidena, a town of Latium, five miles from Rome, the building subsided, and 20,000 spectators according to Suetonius, 50,000 according to Tacitus, were among the number between killed and wounded.