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.

Francisco de Orellana failed to find El Dorado, but discovered the Amazon. Early in 1541, a rumor swept Quito that beyond the mountains, there lay a land richer than Mexico, or even Peru - a land of gold. The ruler of this land was so rich that he covered himself with gold dust every day and washed it off every evening. He was "the golden man", El Dorado. They had tree goals: to find La Canela, the land of cinnamon: to assess new lands for colonization; and to find El Dorado. On march 1541, They marched eastwards with more that 200 Spanish troops and thousands of native servants.

There are 200 million insects for each of us. They are the most successful animal group ever. Their key is an armoured covering that takes on almost any shape. Darwin's stag beetle fights in the tree tops with huge curved jaws. The camera flies with millions of monarch butterflies which migrate 2000 miles, navigating by the sun. Super slow motion shows a bombardier beetle firing boiling liquid at enemies through a rotating nozzle. A honey bee army stings a raiding bear into submission. Grass cutter ants march like a Roman army, harvesting grass they cannot actually eat. They cultivate a fungus that breaks the grass down for them. Their giant colony is the closest thing in nature to the complexity of a human city.

Plants' solutions to life's challenges are as ingenious and manipulative as any animal's. Innovative time-lapse photography opens up a parallel world where plants act like fly-paper, or spring-loaded traps, to catch insects. Vines develop suckers and claws to haul themselves into the rainforest canopy. Every peculiar shape proves to have a clever purpose. The dragon's blood tree is like an upturned umbrella to capture mist and shade its roots. The seed of a Bornean tree has wings so aerodynamic they inspired the design of early gliders. The barrel-shaped desert rose is full of water. The heliconia plant even enslaves a humming bird and turns it into an addict for its nectar.

The Arctic and Antarctic experience the most extreme seasons on Earth. Time-lapse cameras watch a colony of emperor penguins, transforming them into a single organism. The film reveals new science about the dynamics of emperor penguin behaviour. In the north, unique aerial images show a polar bear swimming more than 100km. Diving for up to two minutes at a time. The exhausted polar bear later attacks a herd of walrus in a true clash of the Titans.

Painting became an important means of communication for David since his face was slashed during a sword fight and his speech became impeded by a benign tumour that developed from the wound, leading him to stammer. He was interested in painting in a new classical style that departed from the frivolity of the Rococo period and reflected the moral and austere climate before the French Revolution. David became closely aligned with the republican government and his work was increasingly used as propaganda with the Death of Marat proving his most controversial work.