During the Second Century the mighty Roman Empire was at the height of its glory. Havin conquered all the known world, Rome seemed made for eternity. But, Samuel Bronston's great epic "THE FALL OF THE ROMAN EMPIRE" began with the death of Emperor Marcus Aurelius (ALEC GUINESS) in 180 A.D., who ruled the Roman world with wisdom and justice. When Aurelius chose a successor in his own family, he sacrified the happiness of millions to his fondness of his weak and licentious son, Commodus (CHRISTOPHER PLUMMER), who succeeded him to the thorne.

The monstrous vices of the tyrannical Commodus led to civil discord and the abandonment of the virtues which had made Rome great. Commodus ignored the counsel of Caesar's Greek philosopher Timonides (JAMES MASON), while inflicting his cruelty on his own sister Lucilla (SOPHIA LOREN), who is in love with the heroic young military Tribune of Rome, Livius (STEPHEN BOYD). After conquering the warring Armenians, Commodus sends word that he will share his throne with Livius as a reward for his great victory. But Livius responds to the enraged Commodus that there must be a new Rome - or a new Caesar.

In Rome, at the height of the Saturnalia festivities, Livius challenges Commodus to summit the Senate to see who will rule Rome. But the Senate supports Commodus, and Lucilla makes a vain attempt to kill the evil Commodus before he can have Livius killed. Commodus orders Livius to be burned at the stake in the Roman Forum, with Lucilla chained at his side. Preparing to set the pyre ablaze, Commodus tells Livius he has not forgotten that he once hailed him as undoubted Caesar and he wishes to repay his debt. He suggests they fight each other with javelins and let the Gods decide whorn they wish to rule Rome...