In episode two, we discover the golden age of the La Tene Celtic warrior and reveal how their world extended as far as central Turkey. But by the middle of the first century BC, the Celts were under threat from an expanding Roman Empire, and the Gallic warrior Vercingetorix would challenge Julius Caesar in an epic battle that would shape the future of Europe.

For most of our history, we humans considered ourselves unique. But now, a new, artificial species might challenge our superiority. Mechanical beings have the potential to change everything. How we got them is a story of astonishing twists and amazing turns to achieve us the machine that may turn out to be the most revolutionary technology ever conceived--the robot.
Learn how robots were first conceptualized in ancient Rome and see how their use has evolved over the centuries, from the calculator to the Mars Lander. Then, take a sneak peek at what future robots will be able to do. Narrated by Patrick Stewart.

This episode tells the story of the Jewish Revolt, which swept through Judea in AD 66 and threatened to destabilise the whole empire. Rome turned to the disgraced General Vespasian and his son Titus to put it down. Filled with spectacular sieges and huge set-piece action, the film pits the discipline and ingenuity of the Roman army against the passion and commitment of the rebels.

This episode tells the story of how the Emperor Constantine brought Christianity to the western world. In AD 312, Rome was in crisis. The empire had been divided into four parts, each with its own emperor who fought one another. Constantine intervened and united Rome, using military might and a new religion - Christianity.

In AD 410, the Goth hordes sacked the city. This event symbolised Rome's collapse. Within 70 years, the western empire - what we think of as Ancient Rome - was abandoned. But it should never have happened at all.

Sagan discusses comets and asteroids as planetary impactors, giving recent examples of the Tunguska event and a lunar impact described by Canterbury monks in 1178. It moves to a description of the environment of Venus, from the previous fantastic theories of people such as Immanuel Velikovsky to the information gained by the Venera landers and its implications for Earth's greenhouse effect. The Cosmos Update highlights the connection to global warming.