This photo is taken on the outside of the theater. Notice the opening is VERY large and even splits into two (Y) and another opening on this side. Roman design engineers knew of a principle (recently discovered called a Venturi) where fluids (air) would naturally move from the side where the hole was small to where the hole was large. This meant air would move up from the stage bringing sound and voices with it and also cool the people sitting in the seats. Natural sound and air conditioning.

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