Tiberius Sempronius Gracchus first makes a mark on history winning the golden crown from General Scipio Aemilianus by being first over the wall at the victorious Battle of Carthage. Back in Rome, now the "capital of the world", he finds the growing gap between rich and poor threatening the foundations of the republic. Urged to achieve greatness through further military exploits, he sets out with reinforcements for the campaign of General Gaius Hostilius Mancinus against the rebellious Numantine tribe in Spain but is defeated and forced to negotiate a peace treaty that the Senate later refuses to ratify. His actions, while repudiated in the Senate, have made him a hero amongst the Roman people and his new father-in-law Senator Appius Claudius Pulcher supports him in a successful campaign to become their Tribune. He snubs the Senate and takes his proposed land reforms directly to the People's Assembly, where his old friend Octavius vetoes them. He brings the city to a standstill when he vetoes all other business in response and has Octavius deposed. Octavius and the Senate spread false rumours that he intends to make himself king and in the ensuing unrest he is murdered.

At the close of the Gallic Wars, Gaius Julius Caesar finds his army encircled by a massive force of Gauls but wins a decisive victory with a brilliant counterattack at the Battle of Alesia. An inspiring speech to his troops, promising to rescue Rome from its corrupt rulers and restore it to its people, raises opposition from Senators Cato and Marcellus. Caesar refuses to disband his army before crossing the Rubicon, plunging the Republic into civil war and turning his deputy Labienus and old friend Pompey against him. Caesar captures Rome unopposed after Pompey is forced to withdraw his vastly outnumbered legions and the senators and people flee. Caesar seizes the emergency funds from the treasury to fund his campaign, but, failing to pay off his soldiers, is later forced to decimate his own rebellious Ninth Legion. Pompey amasses a huge army in Greece while Caesar leads a one-year campaign against opposition in Spain. In Greece, Caesar is forced to retreat inland by Pompey at the Battle of Dyrrachium but is victorious when the Senators force Pompey into an impetuous attack at the Battle of Pharsalus. Caesar overturns the Republic and has himself made dictator for life (essentially the first emperor), only to be assassinated by rivals just four years into his rule.

Nero witnesses the Great Fire of Rome from his villa in Antium and hurries back to the capital to try to control the fire and save lives. Seneca tells him to "rule like the gods" and he vows to build an inspirational city of marble and stone on the ruins. The expense threatens to bankrupt the empire and Tigellinus is sent to rob the temples, turning many in the senate against the emperor. The Pisonian conspiracy to assassinate Nero and have Gaius Calpurnius Piso proclaimed as emperor is revealed, and the conspirators, including the trusted Seneca, are executed. Nero inaugurates the biggest arts festival in Roman history with himself at the top of the bill. In the furious throes of increasing megalomania he kicks his wife Poppea to death. A now isolated Nero leaves Rome in the hands of the Senate as he sets out on a debauched tour of the empire. With his reconstruction still incomplete as the money runs out, Tigellinus is ordered to initiate a campaign of forced suicide to dispossess the richest men in the empire. A rebellion rises up and the Senate sentences the fleeing Nero to death, his suicide bringing the Julio-Claudian dynasty to an end.

The First Jewish-Roman War begins when the Jews rise up against their corrupt governor, drive the Romans out of Judea and defeat a counter-attack at the Battle of Beth Horon. The future Emperor Titus is sent to recall his father Vespasian from exile in Greece to lead the legions against the rebels in Galilee. Josephus Ben Matityahu commands the resistance from the city of Jotapata, where many Jews take refuge from Vespasian’s campaign of terror. Vespasian leads a three-week Siege of Jotapata and Josephus is captured. Joesephus predicts that Titus is destined to be emperor. Jerusalem prepares for a final stand under the fanatical Yohanan of Giscala, who murders the more moderate Hanan and unites the rebel factions. Back in Rome the Empire is thrown into chaos when Nero is overthrown and the army turns to Vespasian to be their new Emperor. Titus accomplishes the Siege of Jerusalem by cutting off the city with an encircling wall. Yohanan ignores Josephus’s pleas for surrender and leads subterranean attacks on Roman siege towers that undermine his own walls. Titus leads a bloody assault that massacres the rebels and razes the city.

In Rome the tyrannical Maxentius consults the gods Jupiter, Apollo and Mars to be told that, the enemy of Rome will be defeated, while outside the city Lactantius tries to convince Constantine to convert to Christianity. Constantine initially dismisses Lactantius but, after seeing what appears to be a sign from the Christian god on the eve of the attack, he follows Lactantius' advice to adopt a Christian symbol. The two forces clash at the Battle of the Milvian Bridge, where Maxentius is drowned in the Tiber as a bridge collapses and the victorious Constantine rides into Rome under the Christian symbol. Constantine creates an alliance by marrying his sister Constantia to the Eastern Emperor Licinius, and the two issue the Edict of Milan as a joint decree of religious tolerance. Constantine’s rejection of the Pagan gods and funding of St. Peter's Church turns Licinius and the Senate against him. Senator Bassianus' failed assassination attempt on Constantine ignites a holy war between the eastern and the western empires. Constantine defeats his opponent at the Battle of Chrysopolis and the empire is united under one Christian god at the Council of Nicea.

The Roman Empire is under barbarian assault from Huns and Vandals. Emperor Honorius’s chief general and adviser Flavius Stilicho has negotiated a treaty with the Goth leaders Alaric and Athaulf, but the Emperor has him executed for conspiracy. Honorius orders Olympius to slaughter all Barbarian families within the Empire and the survivors flee to Alaric’s camp. The Goths sweep through Italy to set siege to Rome, trapping the Emperor’s sister Galla Placidia within. Senator Atalus rides to the Imperial capital at Ravenna and Honorius agrees to the Goths' demands. The Goths withdraw but Honorius break the agreement, sending reinforcements to Rome that Athaulf intercepts and eliminates. Alaric speaks directly to the Senate and they elect Atalus as Emperor, but Honorius has Rome’s grain supplies cut off and Atalus loses authority. Alaric travels to meet Honorius at Ravenna but is ambushed by his old rival Roman General Sarus, who is beaten into retreat. Alaric finally takes Rome, and captures Galla Placidia. Following Alaric’s death, Athaulf marries Galla Placidia and his people finally settle in Southern France.