Hamartia, (Flaw or error of judgement), occurs near the start of the film. It occurs after the scene where emperor Marcus Eraliese tells his son, Comidas, that the throne will be passed down to Maximus instead of him. (Going against the natural order). Comidas kills his father to take the throne. When Comidas announces the “natural caused” death of his father to Maximus, he asks Maximus to stand by him. This is where Maximus’s error of judgement takes place. Maximus refuses to follow Comidas and suffers the consequences. This results in… blah blah blah.
His ‘reversal of fortune’ occurs when he is picked up at the grave of his mother and son and turned into a slave.