The Flavian Amphitheatre, commonly known as the Colosseum, is perhaps the most spectacular monument of classical Rome. It rises between the Esquiline, Coelian and Palatine hills in the place where earlier the artificial lake in Nero's Domus Aurea had been situated. From the aesthetic angle it rounded off the Forum's perspective and became the ideal transit point to other majestic monuments on the hills beyond. It is said that it was built by a certain Gaudentius and that the poor man did not long enjoy the fruits of his labours: he ended his life inside, ad bestias.

Begun by Vespasian (69-79), the first emperor of the Flavian family, in AD 72, the construction works lasted more than ten years; the amphitheatre, still unfinished, was inaugurated in the year 80 under Vespasian's successor Titus (79-81) with fabulous feasting and spectacles which, according to the poet Martial, lasted for a hundred days. It was completed by the third Flavian emperor Domitian (81-96), and restored over a century later by Septimius Severus (193-211).

For many centuries the Colosseum was the symbol of Rome's greatness and power. In it were held continuous combats among gladiators, perhaps the spectacle best liked by the Roman people: people went with a real blood-lust to watch the fights, which would culminate in the solemn and theatrical moment when the fallen gladiator would die at the hands of his adversary. Gladiators' fights continued to around the year 404 (those among animals lasted until the 6th century).

It is understandable that Christian morals should clash with such an inhuman atmosphere and that this should not go unnoticed: thus the physician Galen, who died around the year 200, would praise splendid aspects of Christian morality such as chastity, continence and contempt for death, pointing to individuals among the Christians who were masters of themselves, fervently devoted to noble things which were greatly superior to those pursued by the philosophers. Galen himself was a Stoic rather than a Christian.

The amphitheatre has been damaged several times by serious earthquakes; later the Roman Frangipani and Anibaldi families made it their stronghold until, in the year 1312, the Colosseum became again the property of the Roman people. It decayed during successive centuries; its enormous stone blocks were removed and used in other constructions; finally, in 1750, Pope Benedict XIV declared it a holy place on account of having been the theatre of Christian martyrdoms and thus saved it from further despoiling. A black wooden cross commemorates the faith and fortitude of the martyrs; among them could be mentioned St Ignatius, bishop of Antioch and disciple of St John, sent to the beasts under Trajan (98-117).

The amphitheatre has an elliptical shape, 188 m by 156 m, and is 57 m high. The exterior structure is made entirely of Travertine stone and is arranged into four storeys. The blocks of the base of the pillars are each two cubic metres and weigh five tonnes. The first three storeys are made of eighty semicircular arches divided by pilasters with half-columns following the established sequence of styles: Doric style in the first storey; Ionic style in the second and Corinthian style in the third. The fourth storey is a solid wall decorated with Corinthian pilasters and small windows. In the cornice that crowns the work can still be seen the holes where the poles that held the awning were inserted; this protected the spectators from the sun and it was erected by the sailors from the imperial fleet of Misenus. The fact that there was a detachment of 100 sailors from the fleet in barracks near the amphitheatre who were exclusively concerned with the awning's maintenance illustrates the size and complexity of setting it up.

Every arch on the ground floor had an entrance to the corresponding sector in the amphitheatre: seventy-six of those entrances were numbered and the Roman numbers over the arches are still visible. The four main ones were reserved: one for the imperial court, another for the Vestals, a third for the judges and the fourth for the guests of honour. All the arches on the second and third floor were decorated with statues which have been lost. When the Colosseum became a source of construction materials in the Middle Ages, they removed the metal staples that held the stone blocks together, leaving the countless holes still visible today. On the esplanade in front of the amphitheatre there was a statue of Nero in gilt bronze almost 30 m high, and it has been suggested that this Colossus gave rise to the amphitheatre's name.

The amphitheatre could accommodate some 50,000 spectators, who were arranged in the galleries according to social class. There were three levels of positions: the podium was the first level, reserved for the higher class and the emperor's tribune; the central level was for middle class citizens and the highest level, the summa, was for the people.

The entire floor, made of wooden boards, was covered in sand; around there was a net to protect spectators. Under the sand there was a system of cells, galleries, stores, chambers and underground passages, which we can today see thanks to the excavations. There were a number of rooms where utensils and machinery were kept and also the animals were locked up after the shows. The main shows were the ludi (literally games) or fights to the death among gladiators and the hunting of exotic beasts such as lions and leopards, but the arena was also used for juggling exhibitions, athletic competitions, horseback tournaments and simulated naval battles.