"The Colosseum No matter how many postcards you've seen ofRome's iconicColosseum, you just don't get it until you pass beneath its crumbling arches. Built by Emperor Vespasian in 72 C.E., the huge amphitheater held 50,000 spectators and marked its opening with 100 days of brutal spectacles like gladiator combat and animal fights. The Colosseum was in use for four centuries, and now you can tour the ruins. Walk through the Hypogeum, an intricate series of tunnels and elevators originally used to transport animals, slaves, and gladiators, to the performance above, or take a moonlit tour to have one of the world's most storied structures all to yourself."