From the architectural point of view, the Colosseum is an ellipse of 188 by 156 meters, for a total of 527 meters in circumference, almost 50 meters high: externally starting from a stylobate of two steps there are four floors, three of which with arches framed by semi-columns of different orders, from bottom to top, Tuscanic (similar to Doric but with the base), Ionic and Corinthian. The fourth floor is composed of a kind of attic divided by Corinthian pilasters: in the spaces thus framed square windows open alternating with shields in relief. In each space there are three travertine shelves, corresponding to as many holes made in the end cornice of the structure. All this system was used to support the poles necessary to hold the large clove curtain that was stretched by some sailors of the fleet stationed in Miseno to protect the spectators. At the top, the structure was completed by a cornice with three bands and a molding with a grandiose drip. The outer wall is not complete: what remains is incorporated in the retaining walls built by Valadier in 1820 by order of Pius VII.
All the holes that "move" the structure are due to the medieval removal of the metal pins that were used to hold the travertine blocks that covered everything. Inside, then, the structure is divided into segments by some wedges starting from the base: the aforementioned pillars, connected by arches and rampant vaults, supported the cavea. The advantage was in being able to allow more sites to continue independently in the construction of the same structure, practically divided into four main sites and in their own right. Undoubtedly a wonderful example of organization and planning of the work to be carried out. The basement is divided by three concentric walls and the consequent three annular corridors: towards the center the walls become rectilinear and parallel to the central axis, which is also a corridor. The latter extended in two directions, east and west, even outside the structure: the east branch reached one of the most important gladiatorial barracks known, the Ludus Magnus, still visible today at the intersection between via Labicana and via di S. Giovanni in Laterano. Also outside the majestic structure of the Colosseum there are some travertine stones, discovered in 1895, inserted into the pavement also in travertine: concentric with the same building, they were to mark the area of ??respect. According to another interpretation, they were used to board the ropes of the velarium on the ground.