Ancient Greek theaters were specially constructed to perfectly suit the art which they housed (although without roofs). The multi-thousand-seat theaters were built into hilsides to allow for minimal construction and also excellent accoustics.
In today’s theater, sound is almost always electronically amplified to permit better hearing by the audience, but not having this as an option, these grecian temples had to be constructed perfectly.
By encircling the orchestra with a mathematically perfected design of wooden or stone benches, sloping upwards away from the performance, the ancient architects nearly mimiced the way that sound travels as it spreads. This near-perfect acoustical environment allowed the actors’ voices to travel all the way to the last row of seats.
Also, the Skene buidling which stood behind the orchestra may have assisted in the amplification by reflecting voices and sound towards the thousands of audience members. This arrangement meant that the words which were spoken and sounds of music and dancing were clear such that their importance could be heard accurately.