Gibbon, in Chapter XII of Decline & Fall, provides us with an eloquent description – but whenever is he not eloquent? – of the games and the colosseum (Spectacles of Rome and The amphitheatre).
"...Posterity admires, and will long admire, the awful remains of the amphitheatre of Titus who so well deserved the epithet of Colossal..."
In a footnote, he refers to Maffei, Verona Illustrata, p. iv. l. i. c. 2. I could not find this online, but instead, there is a Piranesi illustration, c.1760.
For detailed information on the Colosseum, one can go to Lacus Curtius, which has both Amphitheatrum Flavium (Platner's) and a more general Amphitheatrum (Smith's Dictionary), the latter with drawings and photos.
There is also a paper (pdf format) titled The Amphitheatre Construction Problem.
