We see a woman tied up in the Coliseum as crocodiles are set loose on her. They are clearly alligators (broad snout), which were unknown to Europeans until Columbus's time, 15 centuries later. Only two countries have alligators: The United States and China.The Romans never went to either place.
Nero's pet dogs are two Arabian Salukis, one of the few modern breeds that can trace its lineage to ancient times. However, that particular breed was unknown in Europe until the 12th Century, when returning Crusaders introduced them for the first time.
As the Christians are holding their clandestine meeting at the Grove, right before the little girl asks her mother "Why don't they sing loud?", the shadow of the boom mic can be seen hovering over the people in the background.
When the boxers are fighting with the spiked gloves, the loser gets punched in the face. He is shown with scars on his face and spits blood onto his chest. In the next shot (from a slightly different angle) the scars are there but the blood on his chest is gone.
A gorilla is seen menacing a chained Christian woman in the arena but in reality gorilla's where not seen until 1856-59 when explorer Paul Du Chaillu became the first westerner to see a live gorilla during his travel through western equatorial Africa .