Short answers, pulled from the story.
The name Colosseum derives from a colossal bronze statue of Emperor Nero known as the Colossus Solis that once stood nearby. This statue was moved to the amphitheater's entrance by Emperor Hadrian in the 2nd century AD, and the structure eventually inherited the name derived from the statue. By the year 1000, the Latin term Colosseum had been coined to describe the amphitheater, originating from the adjective colosseus, meaning gigantic.
Construction of the amphitheater began in 72 AD under Emperor Vespasian and was completed in 80 AD under his successor Titus. The project was funded by the opulent spoils taken from the Jewish Temple after the First Jewish-Roman War in 70 AD, utilizing a massive workforce that included slaves and prisoners of war alongside professional Roman builders.
The Colosseum is an elliptical structure measuring 189 meters in length and 156 meters in width, with an outer wall standing 48 meters high. It was built using travertine limestone, tuff, and brick-faced Roman concrete, held together by 300 tons of iron clamps that were later pried out by stone robbers.
The hypogeum is a two-level subterranean network of tunnels and cages ordered to be built by Emperor Domitian that housed gladiators and animals before contests began. This underground structure included eighty vertical shafts providing instant access to the arena for caged animals and scenery pieces, along with elevators and pulleys to raise and lower them to the surface.
Following the decline of gladiatorial games, which were banned by Honorius in 399 and last mentioned around 435, the Colosseum underwent radical changes in use. By the late 6th century, a small chapel had been built into the structure, and the arena was converted into a cemetery before the Frangipani family fortified the building in the 13th century.
The Colosseum has become a symbol of the international campaign against capital punishment, with the local authorities of Rome changing the color of the Colosseum's night-time illumination from white to gold whenever a person condemned to the death penalty has their sentence commuted or a jurisdiction abolishes capital punishment.