On Architecture

4. The roof of the colonnade to be built at the top of the rows of seats, should lie level with the top of the “scaena,” for the reason that the voice will then rise with equal power until it reaches the highest rows of seats and the roof. If the roof is not so high, in proportion as it is lower, it will check the voice at the point which the sound first reaches.

5. Take one sixth of the diameter of the orchestra between the lowest steps, and let the lower seats at the ends on both sides be cut away to a height of that dimension so as to leave entrances (0, P). At the point where this cutting away occurs, fix the soffits of the passages. Thus their vaulting will be sufficiently high.