<human>:  When did the Romans start building the Colosseum?
<bot>: The Colosseum was built between 72 and 80 AD. The first stone was laid in 72 AD by Emperor Vespasian, and it was completed in 80 AD. The Colosseum was the largest amphitheater in the world, and was used for gladiator fights, animal hunts, public executions, and public spectacles. It was also used for concerts and musical performances.