The most internationally recognized symbol of Rome, the Colosseum has a long and bloody history. It was inaugurated in 80 A.D. with 100 days of games, including gladiatorial combats and animal fights. It was the largest amphitheater in the Roman Empire and is believed to have packed up to 50,000 people inside. Despite centuries of neglect—it was used as a quarry until the eighteenth century—it has remained intact (for the most part).
Today nearly 4 million people visit annually. Buy your tickets in advance or be prepared to wait in a very long line. A combined ticket for the Roman Forum, Colosseum, and Palatine Hill grants access to all three sites and lets you skip the line at the Colosseum.