In this historical drama, the turbulent transition from Roman republic to autocratic empire, which changed world history through civil war and wars of conquest, is sketched both from the aristocratic viewpoint of Julius Caesar, his family, his adopted successor Octavian Augustus, and their political allies and adversaries, and from the politically naive viewpoint of a few ordinary Romans, notably the soldiers Lucius Vorenus and Titus Pullo and their families.
'The Stolen Eagle.' In Gaul in 52 B.C., two Roman soldiers, Legionary Titus Pullo and Centurion Lucius Vorenus, are tasked with recovering Julius Caesar's personal Eagle, stolen from his camp in the dead of night. With his campaign in Gaul coming to a successful conclusion, Caesar's popularity is continuing to grow. He's saddened however when he receives news from his good friend Pompey Magnus that his daughter, Pompey's wife, has died in childbirth. In the Senate, Pompey must defend the prolonged absence of his friend and co-Consul Caesar against charges of corruption.

Caesar winters his army in Gaul near the Italian border while his enemies in Rome fear that he will do something no Roman General has done: cross the Rubicon with his army. To counter-balance his opponents, Caesar puts his friend Mark Antony up for office as the people's Consul. Vorenus and Pullo accompany Mark Antony and Octavian to Rome. For Pullo, it's an opportunity to get drunk and ravish every woman in sight.

Caesar contemplates Pompey's counteroffer but Mark Anthony wishes the war. Vorenus continues to struggle as a businessman and must reevaluate his career choice. Atia schemes to come between Caesar and Servilia and Pullo seeks Octavian's help.

Caesar pursued Pompey to Greece but the tide has turned and it's Caesar who is on the run. He contacts Mark Antony, who he left in charge in Rome, to come and join him with the 13th Legion but Antony seems to be in no hurry.
Vorenus has re-enlisted in Antony's Legion and he and Niobe have begun to renew their marital relationship. The presence of Niobe's sister is the only sour note in their house. Pullo meanwhile continues to train young Octavian in the use of arms and the boy's mother Atia is so pleased with his development that she decides he should take another.

The defeated Cato and Scipio fall back on the African city of Utica after the Battle of Thapsus where they decide to end it all. Caesar, after two years of fighting in Greece and Egypt, returns to Rome and receives a hero's welcome.
Meanwhile, Servilia's cold rage against the Julii clan makes Brutus's submission to Caesar even more painful. Octavian returns home from military school and Caesar, impressed with his nephew's incisive political acumen, appoints him a pontiff despite his youth.

Rejected by Vorenus and Eirene and racked by guilt for the killing of Eirene's fiancé out of a jealous rage, Pullo has sunk to working as an assassin for the gangster Erastes. When Pullo gets arrested for killing one of Caesar's popular opponents, he condemns himself by refusing to name who hired him, despite Octavian's attempts to defend him.
Meanwhile, Vorenus finds his new official duties as magistrate tedious, especially when he gets caught between Caesar and the demands made by veterans' spokesman Mascias.