The Colosseum was used by the emperors to show off their power, wealth and to support their popularity. The show was usually held for more than one day and it included comical acts, displays of exotic animals and fights to the death between animals and gladiators or between gladiators.
The fighters were slaves, condemned criminals, prisoners of war, free Romans and even Emperors. In fact, the only emperor to participate in this kind of fights was Commodus. He killed but was never killed because his opponents were under-armed, poorly skilled or existed from previous fights. He was portrayed in the movie, Gladiator.
If a gladiator was victorious in many fights he had the right to implore the emperor for his liberty. If his request was accepted, the gladiator was given a wooden sword, as a sign that he was a free man and would never have to fight again.