Germania, 180 A.D. The Roman Army is stationed at the edge of a burnt and devistated meadow. Everyone is tense and impatient for the battle that's ready to start any moment against the desperate barbarians. General Maximus and his second in command, Quintus, are talking when shouts come from down the lines. The messanger, the last hope for a peaceful surrender, has returned headless. The barbarian chief walks out of the forest carrying the head of the unfortunate legionaire. Now it's time for battle. Maximus heads off to join the calvary while Quintus stays to command the rest. When Maximus' signal flare is seen, the army starts out across the field towards the treeline, now full of angry, bloodthirsty natives. As the last battle begins, Emperor Marcus Aurelius stands watch from a safe hilltop position. This is his last battle; he wants to leave the frontier safe. It's a bloody fight, and many on both sides fall. Finally, when it's over, the Romans stand triumphant. It's all for the glory of Rome.
In a royal wagon sit brother and sister, Commodus and Lucilla. Their father, Marcus, has asked them to join him in Germania. Commodus is sure that the Emperor will anounce him as his successor. When the caravan stops, Commodus orders for his horse and heads for the front. Apon his arrival, he finds that the battle is already done, and that Maximus is getting the tribute for it. Irritated, he tries to make himself look better by giving his arm to his father as he walks. Marcus, on the otherhand, decides not to, and mounting his horse with the help of Maximus, rides away.
Later, Marcus asks that Maximus see him in his tent. He has an important job for the general: after he is dead, he wants Maximus to become the "Protecter of Rome". Instead of a new Emperor, Marcus wants the government to return to a republic. Maximus is unsure of what to do and leaves the old man with mixed feelings. On his way out he runs into a familiar face, Lucilla. They have a brief, awkward discussion, and Maximus leaves her.
When Marcus tells Commodus that he will not become the next Emperor and that Maximus is to look after things, he can't bear it and suffocates his father. When Maximus comes to see the body, he knows that something is not right and prepares to fight. However, Commodus is one step ahead. He orders the execution of the general. Quintus stands by unhelping as the soldiers drag Maximus from his tent. When they stop riding at dawn, they prepare to execute him. He has other plans, however, and is able to escape, although wounded. Knowing that Commodus has send soldiers to kill his family, Maximus heads for home. But he arrives too late; his wife and son are already dead. Exhusted and weak, a passing caravan headed for the Roman province of Zucchabar picks him up. When they arrive, Maximus along with others, are sold to Proximo to be trained and fight as gladiators.
Maximus eventually wins the approval of the crowd and his fellow gladiators and Proximo decides he has a good chance at the 150 day gladitoral event being held in Rome. Maximus discovers that Proximo is a former gladiator, freed by none other than Marcus Aurelius. The ex-gladiator has one word of advice for the slave: "Win the crowd, and you'll win your freedom". When they arrive at the Colosseum for their first fight, Proximo's group, the "Barbarian Horde" emerge victorious. The watching Emperor Commodus wants to meet the amazing gladiator who fought so well. When he finds out that it's really Maximus, he's stunned. As the games continue, Maximus becomes even more famous and favoured, and Commodus starts to go mad with hatred and jealousy towards his enemy.
Meanwhile, Lucilla is terrified of her brother and fears for the safety of her son, Lucius, who is heir to the throne. She decides that what is best, both for herself and for Rome, is to dethrone Commodus. To do this, she needs Maximus' help, although he is hesitant to agree to her plans. She has him meet with senator Gracchus, one of the leaders of those who support the idea of a republic. Maximus eventually agrees to help; if he can get back to his army, he can lead them. If he controls the army, he can control Rome. An escape plan is hatched. Now all Maximus has to do in the meantime is stay alive.
Commodus has had the senate members followed and so discovers that his sister and Gracchus are up to something. He has Gracchas arrested and imprisioned, and threatens the life of his nephew if Lucilla does not tell him exactly what is going to happen. When the time comes for Maximus to make his escape, a group of Praetorians try to storm the coumpound in which he is being held. Proximo, up until now unsure of what to do, lets Maximus go. Buying the general some time to get away, Maximus' gladiator commrades fight off the soldiers as best they can. As Maximus makes his way outside he spots his trusted servant, Cicero, waiting with some horses to make their get away. It is a trap, however, and as soon as Cicero yells a warning to his master, the horse is released from under him and is left hanging by the neck. Maximus races to save him, but the poor man in shot in the chest with several arrows.
Caught and in chains, Maximus is held under the floor of the Colosseum. Commodus is there, and has planned a little fight between the two of them. Being the good sport that he is, the Emperor embraces Maximus. As he does, he stabs the general in the back, deeply wounding him. In his degenerating condition, Maximus rises with Commodus to the Colosseum floor. Commodus thinks that this is his chance to show the Roman people that he is just as brave and worthy as their beloved Maximus. As the fight begins, the two mortal enemies fight feriously; Commodus for approval, Maximus for vengence. When Commodus and Maximus are both unarmed, Maximus turns his back on the malicious Emperor. As he does this, however, Commodus reaches up his sleeve and lunges at Maximus with his dagger. Still too quick for him, Maximus turns and fights Commodus. As they struggle, Maximus is able to grab his wrist and turn the dagger towards the Emperor. Slowly, he forces the dagger through Commodus' throat. With one last thrust, he lets Commodus fall to the ground, dead. Silence reigns in the huge arena of fifty thousand spectators. Maximus stumbles slightly, but is able to right himself. He orders Quintus to reinstate Gracchus and to free Proximo's men that were captured during his escape. Then he falls to the ground. Lucilla rushes out and kneels beside her once beloved. Maximus is in a wheat field. He can see a door. He reaches out and opens it. "Go to them," Lucilla says. His family is there. He's joined them in Elysium. As the gladiators gather around their fallen hero, Lucilla asks that they honor him. His friends pick him up and carry him out of the arena, leaving the body of Commodus were it fell.
As the sun is setting, Juba, one of Maximus' freed gladiator friends digs a small hole in the dirt floor of the Colosseum. Inside it he places the small carved figures of a woman and child: Maximus' most prized possessions. As he covers them over with earth he tells himself that he, too, will see his own family soon. But not yet.