At the outer edge circumferential arcades link each level and the stairways between levels. The three tiers of arcades are faced by three-quarter columns and entablatures, Doric in the first story, Ionic in the second, and Corinthian in the third. Above them is an attic story with Corinthian pilasters and small square window openings in alternate bays. At the top brackets and sockets carry the masts from which the velarium, a canopy for shade, was suspended. The Colosseum was designed to hold 50,000 spectators, and it had approximately eighty entrances so crowds could arrive and leave easily and quickly.
Vaults span between eighty radial walls to support tiers of seating and for passageways and stairs.
Resources Sources on Roman Colosseum Robert Adam. Classical Architecture . Penguin Books, 1990. Drawings of Great Buildings . Roger H. Clark and Michael Pause.