The Greek amphitheater is deepened into the ground, the Roman amphitheater (Colosseum) is surrounded by high walls. The Colosseum had removable arenas, under which were complex engineering structures. With the help of special mechanisms, scenery, people and animals, were raised into the arena, which were in underground rooms before the performance.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.