Colosseum's were used for entertainment for all of Rome, like they might have gladiators battling other animals or reenactments of wars and they invited all of Rome to watch.Think of a football stadium that is about what they looked like just none of all the fancy print and there was not grass on the field. Construction on the Colosseum was started in 72 AD by emperor Vespasian. It was finished eight years later in 80 AD. These Colosseum's were massive, they could hold up to 50,000 people.They were so big it took them 8 years just to make one of these huge stadiums. If you are wondering who emperor Vespasian he was the only guy to die of natural causes compared to the rest of his fellow emperors.
The more important you are the closer to the bottom of the Colosseum you got to sit, as shown in the picture below. For example if you were a senator you got to sit at the bottom while if you were a slave or woman you would have to sit at the very tip top where you could barely see the bottom of the Colosseum. They were so big it took them 8 years just to make one of these huge stadiums.