184 
PLATE IV. 
PLAN OF THE THEATRE AT POLA. 
The plan of the theatre of Marcellus, as it is given by 
Piranesi, being incomplete from the want of the scene, the 
plan of a theatre at Pola, which has the scene as well as the 
porticoes behind it in part remaining, is here introduced 
from the plates of Serlio. It corresponds in many particulars 
with the description Vitruvius gives of the Roman theatre, 
such as the position of the scene, and the arrangement of 
the interior. 
Four equilateral triangles are inscribed in the area 
formed by completing the circle of the orchestra. a.a. Are 
those angles which determine the position of the staircases 
between the lower cunei. d.d. The base of the first trigon, 
which is in a line with the front of the scene. b. The valvae 
regiae. c.c. The door-ways, called hospitalia. The line 
a.a. which passes through the centre of the circle divides 
the orchestra, Afrom the proscenium, B. e.e. The entrances 
in the returns of the scene. f.f. The revolving scenes termed 
periacti. g.g. The lower range of seats divided into cunei 
by staircases leading to the first praecinction, h. 
The seats of the senators were arranged in the orchestra, 
which, like that of the Greek theatre, was at first a level 
area; but in after-times a gentle ascent was given to it. The 
benches of the orchestra were termed sedes by Vitruvius in