The Colosseum, also known as the Flavian Amphitheater, was began by Vespasian (70 CE), inaugurated by Titus (80 CE) and completed by Domitian (82 CE). Located on marshy land between the Esquiline and Caelian Hills, it was the first permanent amphitheater to be built in Rome.
The amphitheater is a vast ellipse 189m x156.4m (620ft x 513ft), with eighty external arcaded openings on each story, those on the ground floor forming entrances from which the tiers of seating for 50,000 spectators were reached. The arena proper is an oval 87.47m x 54.86m (287ft x 180ft) surrounded by a wall 4.57m (15ft) high. Below the wooden arena floor, there was a complex set of rooms and passageways for wild beasts and other provisions for staging the spectacles.
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 construction utilized a combination of concrete types: lava for the foundations, tufa and brick for the supporting walls, and pumice stone for the vaults to reduce weight. Travertine blocks, set without mortar and held together with metal cramps, were used in the facade, while marble was employed for the columns, sears and ornament.
Espouy, H. d'. (1905). Fragments d?architecture antique d?apres les releves & restaurations des anciens pensionnaires de l?Academie de France a Rome; publies sous la direction de H. d?Espouy. (Vol. 2). Paris: C. Schmid. Plate 116.