The Colosseum, Rome's most famous landmark, is separated from the Forum by the Arch of Constantine. There are lots of these triumphal arches in Rome, as each emperor liked to commemorate some trumped-up victory by building one. This one tends to be more famous than others because of its ground zero location. Constantine became emperor in the twilight years of Rome, though, so the people couldn't be sufficiently bothered to build a proper arch. Instead they covered the arch with stuff stolen from other arches, and called it a day.

Emperor Nero, of the fiddling while Rome burned fame, used the famous fire as a great opportunity to build the biggest palace the world had ever seen. While his new digs covered much of Rome, he also built a huge lake, and an even huger bronze sculpture of himself near the lake. Clocking in at the equivalent of a ten story building, it was called the Colossus, which as you probably guessed gave the world the words collosal and Colosseum. After his death, the lake was drained and given to the city as a new park, the centerpiece of which was the state of the art Colosseum. The bronze Colossus stayed, with a new head being put on with the coronation of each new emperor. Amazingly, this giant statue somehow disappeared, with no record of anyone ever taking it, melting it down or moving it.