Rome was once a largely democratic society, with regular elections. This Republic lasted for 500 years, but then came Tiberius Gracchus. He believed in the ideals of the Republic - fairness, decency and justice for everyone -but was appalled by Rome's aristocrats' treatment of the poor. So he unleashed the power of the mob upon the streets of Rome, with devastating consequences.

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.

New Zealand - 850 years ago New Zealand was the last major land mass to be discovered and colonised by humans. A mere 850 years ago, Polynesian seafarers arrived in a land with no terrestrial mammals. New Zealand was a land of birds, and its avian rulers were giants: huge herbivorous moas were hunted by Haast's eagle - the largest eagle the world has ever seen. But within the space of only 100-400 years, the eagle, all the moas and over 20 other species of birds were gone. Had mankind become the monster?

Welcome to an extreme landscape of rock, ice and snow. We tour the mightiest mountain ranges, starting with the birth of a mountain at one of the lowest places on Earth and ending at the summit of Everest. Find out how some of the most secretive animals rise to the challenge of mountain life. Share one of Earth's rarest phenomena, a lava lake that has been erupting for over 100 years. The same forces built the Simian Mountains where we find troops of gelada baboons nearly a thousand strong. In the Rockies, grizzlies build winter dens inside avalanche-prone slopes and climb the peaks to devour abundant summer moths. In another world first, the programme brings us astounding images of a snow leopard hunting on the Pakistan peaks.

Jungles cover roughly three per cent of our planet yet contain 50 per cent of the world's species. High-definition cameras enable unprecedented views of animals living on the dark jungle floor. In the Ngogo forest the largest chimpanzee group in the world defends its territory from neighbouring groups. Other jungle specialists include parasitic fungi which infiltrate an insect host, feed on it, and then burst out of its body.