The Colosseum is one of New 7 Wonders of the World and the largest amphitheater that was ever built. It was constructed almost 2000 years ago, completed in 80 AD. In its heyday, between 50,000 and 80,000 spectators would watch gladiator contests, executions, animal hunts, and the reenactments of famous battles.
This is one of Rome's most popular sites to visit, so expect large crowds and long lines. For the best experience, book your tickets in advance. I recommend doing this as soon as you know your travel dates because tickets can sell out.
It takes about one hour to tour the Colosseum. To get the most out of your visit, you can take a tour to areas not included on the regular ticket. Visit the Arena, the Underground (where the animals were kept), and the third tier of the Colosseum.