The origin of this can be traced back the the funerary rituals of the high ranking held in the necropolis by early Italic tribes; this involved sacrificial offerings made to the gods of the underworld, the DII INFERII, in the shape of bloody fights held on top of the grave in order to placate the spirits and help the deceased cross into the afterlife.
These rituals were inherited by the Roman world and during the last two centuries of the republic they changed from being a private to a public spectacle which took place in the amphitheatre. The protagonist were the infamis, those without a legal and social standing, the outcasts of the age, which included pimps, prostitutes, actors, magicians and gladiators, whose body and will were subjected to the wishes and pleasures of others.
Surprisingly some would join the ranks of gladiators through free choice attracted to the world of physical antagonism and the super stardom which experienced fighters would some time achieve. By swearing a special oath “uri, vinciri, verberari, ferroque necari patior“, the auctoramentum depugnandi, these free men would become gladiators Autocratii, willingly surrendering their body to the Inferii Dii, the gods of the underworld.
The night before the fight in the Arena a sumptuous banquet, the Cena Libera, was held for the gladiators in order to purify their blood before the fight so they could become the perfect sacrifice for the goods; this banquet was sometime a private affair and, at other times, the public was allowed to watch with a sense of anticipation and morbosity in the knowledge that for some of the participants this would be the last night on earth.