ClipArt ETC
"Elevation and Section of the Tiers of Seats and Substructure of the same from the Colosseum at Rome. The whole mass of the rows of seats was supported by a solid substructure of piers and arches, which formed passages of three stories one above the other, retaining the circular form of the building; whilst externally they formed arcades, which were surrounded with half-columns or piers with entablatures over them. The exterior of the straight portion of the building, which contained the stage and some chambers connected with it, was generally surrounded by a portico. The theaters were either open, or were protected against the sun and rain by an awning stretched over them."

Elevation and Section of the Colosseum

"Elevation and Section of the Tiers of Seats and Substructure of the same from the Colosseum at Rome.…

"Ground Plan of the Colosseum at Rome, with representation of the Tiers of Seats, and of the Substructure. The shape of the amphitheatre was borrowed from that of the theatre. Since no stage was necessary, and with a view to securing as many rows of seats as possible, the semicircular form of the theatre was done away with, and the whole became a circle, or rather an ellipse, which was afterwards the recognized shape for all buildings of this nature, whether at Rome or in the provinces."

Ground Plan of the Colosseum

"Ground Plan of the Colosseum at Rome, with representation of the Tiers of Seats, and of the Substructure.…