Short answers, pulled from the story.
Construction of the Colosseum began under the Emperor Vespasian in 72 AD and was completed in 80 AD by his son and successor Titus. The building was funded by spoils taken from the Jewish Temple after the First Jewish-Roman War in 70 AD.
The Colosseum could hold an estimated 50,000 to 80,000 spectators at various points in its history, with an average audience of around 65,000. The Codex-Calendar of 354 placed the figure as high as 87,000.
The Colosseum hosted gladiatorial contests, animal hunts known as venationes, public executions, re-enactments of famous battles, dramas based on Roman mythology, and in its early years, simulated sea battles called naumachiae. Animal hunts continued until at least 523 AD.
The Colosseum was damaged by a major fire in 217, caused by lightning, and by severe earthquakes, most significantly one in 1349 that brought down the entire outer south wall. Stone and iron clamps were systematically removed for use in other buildings across Rome throughout the medieval period.
Christians generally regard the Colosseum as a site of martyrdom during Roman persecutions, and Pope Benedict XIV consecrated it in 1749 to the Passion of Christ. However, the Catholic Encyclopedia notes there is no direct historical evidence that large numbers of Christians were martyred specifically at the Colosseum rather than elsewhere in Rome.
Rome's local authorities change the Colosseum's night-time lighting from white to gold whenever a person facing the death penalty anywhere in the world has their sentence commuted or a jurisdiction abolishes capital punishment. The lights changed in November 2012 following Connecticut's abolition of the death penalty in April 2012.