Major Bill Cage is an officer who has never seen a day of combat when he is unceremoniously demoted and dropped into combat. Cage is killed within minutes, managing to take an alpha alien down with him. He awakens back at the beginning of the same day and is forced to fight and die again... and again - as physical contact with the alien has thrown him into a time loop.
After the death of Emperor Marcus Aurelius, his devious son takes power and demotes Maximus, one of Rome's most capable generals who Marcus preferred. Eventually, Maximus is forced to become a gladiator and battle to the death against other men for the amusement of paying audiences.