The plan of the theatre itself is to be constructed as follows. Having fixed upon the principal centre, draw a line of circumference equivalent to what is to be the perimeter at the bottom, and in it inscribe four equilateral triangles, at equal distances apart and touching the boundary line of the circle, as the astrologers do in a figure of the twelve signs of the zodiac, when they are making computations from the musical harmony of the stars. Taking that one of these triangles whose side is nearest to the scaena, let the front of the scaena be determined by the line where that side cuts off a segment of the circle, and draw, through the centre, a parallel line set off from that position, to separate the platform of the stage from the space of the orchestra.
The platform has to be made deeper than that of the Greeks, because all our artists perform on the stage, while the orchestra contains the places reserved for the seats of senators. The height of this platform must be not more than five feet, in order that those who sit in the orchestra may be able to see the performances of all the actors. The sections (cunei) for spectators in the theatre should be so divided, that the angles of the triangles which run about the circumference of the circle may give the direction for the flights of steps between the sections, as far as up to the first curved cross-aisle. Above this, the upper sections are to be laid out, midway between (the lower sections), with alternating passage-ways.
The angles at the bottom, which give the directions for the flights of steps, will be seven in number; the other five angles will determine the arrangement of the scene: thus, the angle in the middle ought to have the “royal door” opposite to it; the angles to the right and left will designate the position of the doors for guest chambers; and the two outermost angles will point to the passages in the wings. The steps for the spectators’ places, where the seats are arranged, should be not less than a foot and a palm in height, nor more than a foot and six fingers; their depth should be fixed at not more than two and a half feet, nor less than two feet.