Sacrifices at the Roman Colosseum - The Altar
A marble altar would have been set in the middle of the arena complete with a fire burning on the altar. The altar was dedicated to the worship of of Diana, Pluto or Jupiter Latiaris. The worship of  Jupiter Latiaris involved human sacrifice and it is possible that a bestiarius was sacrificed at the opening of the early Roman games. Animal sacrifice was more common. The sex of the sacrificial animal had to correspond to the sex of the deity to whom it was offered. White animals were sacrificed to the gods of the upper world  whereas black victims to the deities of the under world. A bull or an ox was the most common animal selected for sacrifice.

Sacrifices at the Roman Colosseum - The Sacrifice and Ceremony
The religious ceremony was conducted in the centre of the arena by priests dressed in white robes and red scarves who would sprinkle incense on to the fire. A solemn procession of priests began with a  procession (Latin pompa) into the arena with carriages holding statues to the gods. The sacrificial animal would also be led into the arena. The words of the religious ceremonies were of vital importance as was the choice of an appropriate offering.

Sacrifices at the Roman Colosseum - The Games begin
After the animals had been ceremoniously sacrificed the priests would examine their entrails and declare that the gods wished the games to proceed. The religious procession would then leave the arena swinging incense burners and chanting hymns. Slaves would quickly remove the altar and the carcasses of the animals. The games festival was now able the begin.