After only a decade of construction the Colosseum opened in A.D. 80 with a festival including 100 days of games. The finishing touches of construction of the Colosseum were completed under the reign of Titus' brother and successor, Domitian.
Measuring some 620 by 513 feet, the Colosseum was the largest amphitheater in the Roman world. Unlike many earlier amphitheaters, which had been dug into hillsides for support, the Colosseum was a freestanding structure made of stone and concrete. The exterior consists of three stories of arched entrances supported by semi-circular columns. Each story contained columns of a different order (or style): At the bottom were columns of the relatively simple Doric order, followed by Ionic and topped by the ornate Corinthian order. Located just near the main entrance to the Colosseum was the Arch of Constantine, built in A.D. 315 in honor of Constantine I's victory over Maxentius at Pons Milvius.
Inside, the Colosseum had seating for more than 50,000 spectators, who may have been arranged according to social ranking but were most likely packed in any way they would fit. Awnings were unfurled from the top story in order to protect the audience from the hot Roman sun as they watched gladiatorial combats, hunts, wild animal fights and larger combats such as mock naval engagements (for which the arena was flooded with water) put on at great expense. The vast majority of the combatants who fought in front of Colosseum audiences in Ancient Rome were men (though there were some female gladiators). Gladiators were generally slaves, condemned criminals or prisoners of war.
The Colosseum saw about 4 years of actual use, until the struggles of the Western Roman Empire and the gradual change in public tastes put an end to gladiatorial combats and other large public entertainments by the 6th century A.D. By that then, the arena had already suffered damaged due to natural phenomena like earthquakes and such. In the next few centuries, the Colosseum was abandoned completely, and used as a quarry for numerous building projects, including the cathedrals of St. Peter and St. John Lateran, the Palazzo Venezia and defense fortifications along the Tiber River.
During the 18th century various popes sought to conserve the arena as a sacred Christian site, though it is uncertain whether early Christian martyrs met their fate in the Colosseum.
By the 20th century, a combination of weather, natural disasters, neglect and vandalism had destroyed more than half of the original Colosseum. Efforts to restore the structure began in the 1990s, and have proceeded over the years, as the Colosseum continues to be a leading attraction for tourists from all over the world.