The Colosseum is elliptical, measuring 189 m (620 ft) long and 156 m (513 ft) wide. Its exterior, 47 m (157 ft) high, is a three-storied arcade surmounted by a fourth story pierced with windowlike openings. Each of the three arcaded stories originally had 80 arches. A broad pavement of travertine (a whitish calcium carbonate frequently used as building stone), bordered by travertine posts, once surrounded the entire Colosseum, which was entered through the arches of the lowest arcade. The outer wall and the skeleton of the interior up to the second story were constructed of large blocks of travertine bonded with metal. Elsewhere, softer stones, concrete, and bricks were used.
The openings of the surviving arches of the Colosseum are framed with impressive but nonfunctional engaged columns and entablatures of the Tuscan, Ionic, and Corinthian orders (see Column). The fourth story is decorated with Corinthian pilasters and entablatures. In ancient times, statues filled the spaces of the arches, and metal shields were attached to the spaces between the large windows of the fourth story. Above these windows ran a continuous row of consoles in which sockets were cut for the masts that projected upward through corresponding holes in the cornices. These masts supported awnings used to protect the spectators from the sun.
Behind each of the outer arcades, two corridors circled the Colosseum, and beyond these were two other smaller concentric corridors. From the corridors, stairways gave rapid access to all parts of the cavea, which extended upward from the podium, or platform, bordering the central arena. On the podium were marble seats for distinguished spectators, along with individual boxes provided for the emperor and the chief city officials. The cavea was behind the podium and separated from it by a low wall and a passageway. Divided by aisles into wedge-shaped sections, the cavea sloped upward to a high wall, which was pierced with windows to light the corridor behind it. Above this was a gallery of wooden seats, which was covered in the rear with a portico. The seating capacity of the Colosseum is believed by modern scholars to have been about 50,000.
The elliptical arena inside the Colosseum, measuring 280 ft (85 m) long and 53 m (175 ft) wide, was a pit surrounded by a high wall, intended to protect spectators from the wild animals often used in combats held in the arena. Its sand-covered floor was built of wood supported by deep substructures, in which traces of animal dens, elevators, and other mechanisms have been found. Combats between gladiators in the Colosseum were abolished in ad 404, and the last recorded fight between animals was held there in ad 523.
