The Romans took their conception of the theatre from the Greeks. The building was composed of two parts, the one devoted to the stage and its accessories, and the other to the accommodation of the audience. The stage was usually in the form of a rectangle, the longer side of which formed the diameter of the semicircle, which was the plan of the second part. The latter was composed of concentric seats in successive steps, to which access was had by stairs radiating from the centre and leading to an upper surrounding gallery. At the foot of these steps a space was reserved called the orchestra (Greek, “dancing place”), usually occupied by the senators. The stage, which was decorated with columns and niches, was raised above the orchestra, and was connected with the actors’ rooms. The wall at the back of the stage was carried up to the level of the circular enclosing wall, and treated with superposed orders. The theatre of Marcellus, in Rome, and those of Herculaneum, Arles, and Orange are among the best examples. The most celebrated amphitheatre (amphi theatron, Greek, “double theatre”) is that commonly known as the Colosseum, or Flavian Amphitheatre. It is composed of the arena or oval space, occupied by the combatants, and of the “visorium,” formed by concentric seats placed in tiers, one above the other. [Illustration: PLAN OF THE TEMPLE OF THE SUN AT BAALBEK.] It was capable of seating eighty thousand spectators, and upon its arena four thousand gladiators have fought at a time. It was here that before commencing their combats they came to the foot of the emperor’s throne, saluting him with the celebrated cry, “Morituri te salutamus.” The substructure of the building consists of vaulted passages, communicating with the visorium by numerous staircases, and with the exterior by the doors called “vomitoria.” The arena was surrounded by a ditch of running water, and under it were chambers in which prisoners and animals were confined. The visorium was divided according to the rank of its occupants. The upper classes occupied the “podium” or lower gallery, which extended on either side of the emperor’s throne, at the extremity of the longer axis of the building. For protection from the elements during performances an immense sail was stretched over the building from posts inserted in stone brackets at the top of the exterior wall. The heights of the three lower stories of the Colosseum are marked externally by arcades and superposed orders with engaged columns, Doric, Ionic, and Corinthian, and the fourth and upper one by Corinthian pilasters. The entablatures of each order are carried around the entire circumference of the building.