A slave or prisoner trained to fight other gladiators, wild beasts, or condemned criminals for the entertainment of the people in ancient Rome. Gladiators belonged to four categories: the Mirmillo, with a fish on his helmet, and the Sammite, both heavily armed with oblong shield, visored helmet, and short sword; the Retiarius, lightly clad, fighting with net and trident; and the Thracian, with round shield and curved scimitar. Thumbs up or down from the crowd spelt life or death for the loser. Formal combat degenerated into butchery watched by huge crowds.