The building’s dimensions are impressive. It measures 189 meters (615 ft / 640 Roman feet) long and 156 meters (510 ft) wide, with a base area of 6 acres (24,000 m2). The height of the outer wall is 48 meters (157 ft), equivalent to a 12-15 story building. The perimeter originally measured 545 meters (1,788 ft). The central arena is an oval (287 ft) long and (180 ft) wide, surrounded by a wall (15 ft) high. The colossal monument could accommodate more than 50,000 spectators who could enter through 80 entrances. It is elliptical in plan.
Above the wooden arena floor, there are other four floors, each one being a complex set of rooms and passageways, stairways and rows of seats. Te upper floors were destined to the lower classes and women. The lowest floor was dedicated to prominent citizens. Below the ground were rooms and cages for wild animals and the mechanical devices. There were passageways between the cages and the arena, through witch the animals could appear to the public.
The Colosseum was covered with a huge awning, the velarium. More than 1,000 men were used to install it by anchor it to the ground. The velarium was used to protect the spectators from the sun.