Emperor Vespasian began construction in 72 AD on the site of Nero's private lake - a deliberate statement that he was returning land to the people. The building was completed by his son Titus in 80 AD, inaugurated with 100 days of games that killed 9,000 animals.

The engineering was revolutionary. The elliptical arena measured 620 by 513 feet. Eighty entrances allowed 50,000 spectators to find their seats in minutes. Underground passages (the hypogeum) contained holding cells, machinery, and animal cages. The velarium - a retractable canvas awning - shaded spectators from the sun. Roman engineers solved problems we would struggle with today.

The day's entertainment followed a schedule: animal hunts (venationes) in the morning, executions at midday, gladiatorial combat in the afternoon. The executions were creative: prisoners were dressed as mythological figures and killed as they 'performed' - Orpheus torn apart by bears, Icarus dropped from a height.

Gladiators were slaves, criminals, or volunteers seeking fame and fortune. They trained in schools and fought in pairs. Death wasn't inevitable - valuable gladiators were investments. But death was common. The crowd could decide the fate of the defeated with a thumbs gesture (which direction meant what is still debated). Approximately 400,000 people died in the arena over 400 years.

The animal hunts were ecological disasters. Lions, elephants, hippos, leopards, bears, and exotic creatures from across the empire were shipped to Rome and slaughtered for entertainment. North African lions and elephants were driven to extinction in the wild. The entire ecosystem of the Mediterranean was depleted to feed the Colosseum's appetite.

The floor could be flooded for naval battles (naumachiae), with small ships fighting in the arena. Trap doors released animals from below. Elevators lifted scenery. The spectacles grew increasingly elaborate as emperors competed to outdo their predecessors. The logistics required military-scale organization.

Gladiatorial combat was banned in 404 AD after a monk named Telemachus entered the arena to stop a fight and was killed by the crowd. Animal hunts continued until 523. The Colosseum fell into disuse, damaged by earthquakes and scavenged for building materials. Two-thirds of the original structure was stripped away for palaces and churches.

Medieval Romans believed the Colosseum was a temple or a fort. Its original purpose was almost forgotten. Only in the 18th century did preservation begin, when Pope Benedict XIV declared it sacred ground where Christians had been martyred (probably a legend - evidence is thin).

Today, the Colosseum hosts 6 million visitors annually. Night illumination turns it golden. Concerts are held in the arena. It appears on Italian currency. The Colosseum is Rome's most recognizable symbol, as famous as the city itself.

But it's a complicated symbol. The Colosseum represents Roman engineering genius and Roman brutality in equal measure. The people who built it also used it to watch mass murder for fun. Walking through the ruins, tourists stand where 400,000 people died for entertainment. The greatest amphitheater in history was a slaughterhouse.