which were nonetheless frequent and spectacularly satisfying to the crowd. The races retained a magical aura through their early association with chthonic rituals: circus images were considered protective or lucky, curse tablets have been found buried at the site of racetracks, and charioteers were often suspected of sorcery. Chariot racing continued into the Byzantine period under imperial sponsorship, but the decline of cities in the 6th and 7th centuries led to its eventual demise. The Romans thought gladiator contests had originated with funeral games and sacrifices in which select captive warriors were forced to fight to expiate the deaths of noble Romans. Some of the earliest styles of gladiator fighting had ethnic designations such as "Thracian" or "Gallic". The staged combats were considered munera, "services, offerings, benefactions", initially distinct from the festival games (ludi). Throughout his 40-year reign, Augustus presented eight gladiator shows in which a total of 10,000 men fought, as well as 26 staged beast hunts that resulted in the deaths of 3,500 animals. To mark the opening of the Colosseum, the emperor Titus presented 100 days of arena events, with 3,000 gladiators competing on a single day. Roman fascination with gladiators is indicated by how widely they are depicted on mosaics, wall paintings, lamps, and in graffiti. Gladiators were trained combatants who might be slaves, convicts, or free volunteers. Death was not a necessary or even desirable outcome in matches between these highly skilled fighters, whose training represented a costly and time-consuming investment. By contrast, noxii were convicts sentenced to the arena with little or no training, often unarmed, and with no expectation of survival. Physical suffering and humiliation were considered appropriate retributive justice for the crimes they had committed. These executions were sometimes staged or ritualized as re-enactments of myths, and amphitheatres were equipped with elaborate stage machinery to create special effects. Tertullian considered deaths in the arena to be nothing more than a dressed-up form of human sacrifice. Modern scholars have found the pleasure Romans took in the "theatre of life and death" to be one of the more difficult aspects of their civilization to understand and explain. The younger Pliny rationalized gladiator spectacles as good for the people, a way "to inspire them to face honourable wounds and despise death, by exhibiting love of glory and desire for victory even in the bodies of slaves and criminals". Some Romans such as Seneca were critical