In 53 B.C. Commander of Gaul Julius Caesar leads four veteran legions, hardened by the victorious campaign, across the Rubicon. Caesar's threat to Rome leads a stunned Pompey to declare him "the enemy of Rome" in the Senate chambers. However, Pompey also knows that there is nothing in the city to stop Caesar's advance. Caesar expects the war with Pompey will prove his toughest but greatest achievement.