The Emperor Vespasian started the construction of the coliseum, or "colosseum" ( "colosseo" in Italian) , about a decade after Nero's reign and the "Great Fire" on Rome in 64 A.D. Vespasian wanted to give a spectacular enhancement to the forum's area and central Roman city life which had depreciated as a public center under Nero's reign.
Titus
The name of this new amphitheatre was initialy the "Flavian Amphitheater" in honor of Vespasian's ancestors. The name "Colosseo", apparently derived from a nearby bronze statue of Nero that was defined as "colossal", was later given at some time in the medieval ages. Vespasian died a year before the completion of the coliseum but it was nevertheless officially inaugurated in 80 A.D. by Titus, one of his sons.
Domitian
A few years later, Domitian (the youngest of Vespasian's son) became Emperor and he expanded the coliseum's construction by increasing it's crowd capacity at the third level. He also commissioned the development of an underground network, also called "hypogeum", of tunnels and cells to contain slaves and wild animals.
The Coliseum was used as a "sport" and drama amphitheatre for about 500 years. Over these years, the coliseum had to receive major repairs, especially after a lightning-caused fire in 217 A.D. Even after the fall of Rome in 476 A.D., although there were no more gladiator fights, it was still used for spectacle kind of events like animal hunting and drama for almost a century. It then eventually loss it's initial entertainment vocation to serve as housing in the early medieval ages. It was even used as a castle at some point by a very influential Roman family (Frangipani).
Pope Benedict XIV
After the great roman earthquake of 1349 A.D., which left large damages on the coliseum, a religious community used the old amphitheatre as a home up until the early 1800's. In the mid 18th century, the Pope Benedict XIV declared the coliseum "sacred" because of the Christian martyrs that apparently perished in the arena in it's earlier history.
Since the 19th century, significant restorations of the coliseum and excavation of it's underground network and it became one of the world's top sightseeing attraction. It is visited every year by millions of tourists. Major work has also been done in the 1990's to counter the effect of stone degradation. The coliseum also stands today as a symbol against death penalty and capital punishment.