By the third century AD, the empire that once ran from Spain to Syria is tearing itself apart from within. This episode of the series picks up the story as civil war, corruption, and a revolving door of short-lived emperors hollow out Roman authority just as barbarian pressure builds on every frontier. It traces how a state that had produced centuries of stability became, by the end of the fourth century, a military machine too fragile to hold its own borders. The centerpiece is 410 AD, when Alaric's Vandals breach Rome itself, the first time the city has fallen to a foreign army in eight hundred years. The film lingers on what the invaders actually find: not the crowded, wealthy capital of legend but empty streets, its population already fled as the empire crumbled around it. Told through narration and historical footage rather than interviews, the episode treats the sack of Rome less as a single catastrophe than as the visible endpoint of decades of internal decay.