Albeit the Emperor hosted the munera during the Imperial period and paid them out of the treasury, they were held on special occasions only, e.g., in the context of a triumph, while the ludi (games), such as the ludi Romani, ludi Plebeii etc., took place regularly during religious festivities. They included chariot races in the circus, processions as well as theater displays. Gladiatorial fights were never a part of these ludi.

Who became a gladiator?

Originally prisoners of war were trained as gladiators in the ludi (here: gladiator schools). The names of the oldest gladiator types, such as thraex (Thracian), gallus (Gaul) and samnis (Samnite), refer to the fact that they used to be fighters of those tribes who fought with their typical weapons.

When a specialization of the types set in, it was no longer necessarily a Thracian who appeared in the arena as a thraex. There were also slaves who were sold to a lanista (owner of a ludus) by their master - later on this became outlawed though - as well as criminals who were convicted ad ludos (to gladiator school). Since gladiators were as popular as our today's sports stars, there were also volunteers - sometimes even of the senatorial class - who signed up at a ludus.

We have to differentiate though between volunteers who just received sword fighting lessons at a ludus and appeared only at the prolusio (pre-fights) with blunt or wooden weapons against a professional gladiator, and those who enlisted as professional fighters. Members of the latter group were no longer listed as property-owning, no longer allowed to hold a public office and could not be called into military service. However, they remained Roman citizens.