Amphitheatre

Amphitheaters were most commonly used for gladiatorial matches which had been adapted from Etruscan funeral rites (munera). By the last 1st century BC, however, the games had lost their ritualistic significance.

Gladiators came from various lots of life. Originally, there were gladiatorial schools, but these came under state control in the 1st century BC to avoid them becoming private armies. The majority of gladiators were either condemned criminals (damnati), slaves, prisoners of war, or volunteers who signed up to do shows for a fee. There were four main types of gladiator:

Murmillo: Fought with a helmet adorned by a fish crest, an oblong shield, and a sword. He usually fought a retiarius.
Retiarius: A lightly armed gladiator with a net, brandishing either a trident or a dagger.
Samnite: Utilized a sword, visor and helmet, and an oblong shield.
Thracian: Combated with a curved scimitar and round shield. 

Various other weapons, women, and sometimes even dwarves were used in the games. Special types of "wild animal matches" (venationes) were introduced in the 2nd Century BC and became very popular. Such bouts included men on foot and on horseback, known as beastiarii, who were usually either criminals, prisoners of war, or trained and paid fighters. Beastiarii fought exotic animals, which eventually led to an extensive trade market. Originally, wild animal matches took place on the morning of the games, the public executions were held at midday, and then the gladiatorial matches. Over time, however, these divisions became blurred, and often many fights would take place at once, giving the appearance of a battle. Other spectacles included mock naval battles (naumachiae), known to take place on artificial lakes, as well as animal performances, accompanied by music.

  Excerpted from http://library.thinkquest.org/26602/entertainment.htm