Millions of tourists photograph the ancient monuments of Rome every year. But is there more to them than people guess? There's new evidence that these ruins were once machines, designed by Rome's emperors to connect their power with the sun. Did Roman emperors harness the power of the universe to awe and terrify the people of Rome? We uncover the last, great mysteries of the ancient world's greatest empire.

Cities are growing at a faster rate than any other habitat on Earth. They may seem an unlikely place for animals to thrive, but they can be a world of surprising opportunity. Leopards prowl the streets of Mumbai, peregrine falcons hunt amongst New York's skyscrapers, and a million starlings perform spectacular aerial dances over Rome. In Jodhpur, langurs are revered as religious deities and in Harar, locals live in harmony with wild hyenas. Many animals, however, struggle to cope in the urban jungle. As the architects of this environment, can humans choose to build cities that are homes for both them and wildlife?

The Celts - one of the world's most mysterious ancient people. In Britain and Ireland, we are never far from our Celtic past but in this series Prof. Alice Roberts and archaeologist Neil Oliver travel much further afield, discovering the origins and beliefs of these Iron Age people in artefacts and human remains right across Europe, from Turkey to Portugal. What emerges is not a wild people on the western fringes of Europe, but a highly sophisticated tribal culture that influenced vast areas of the ancient world - and even Rome". Rich with vivid drama reconstruction, we recreate this pivotal time and meet some of our most famous ancient leaders - from Queen Boudicca to Julius Caesar - and relive the battles they fought for the heart and soul of Europe. Alice and Neil discover that these key battles between the Celts and the Romans over the best part of 500 years constituted a fight for two very different forms of civilisation - a fight that came to define the world we live in today. In the first episode, we see the origins of the Celts in the Alps of central Europe and relive the moment of first contact with the Romans in a pitched battle just north of Rome - a battle that the Celts won and that left the imperial city devastated.

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.

David Attenborough concludes his epic history of the evolution of flight with an exploration of the highly advanced fliers that dominate our skies today – the extraordinarily diverse skills of the birds, and the sonar-guided precision of the bats. He encounters some of our planet’s most remarkable fliers – from peregrine falcons dive-bombing starlings over Rome, to hummingbirds hovering in the cloud forests of Ecuador. In a spectacular finale, he visits Gomantong cave in Borneo to witness the mass exodus of a million bats.

The episode begins with Tyson describing how pattern recognition manifested in early civilization as using astronomy and astrology to predict the passing of the seasons, including how the passage of a comet was often taken as an omen. Tyson continues to explain that the origin of comets only became known in the 20th century due to the work of Jan Oort and his hypothesis of the Oort cloud. Tyson then continues to relate the collaboration between Edmond Halley and Isaac Newton in the last part of the 17th century in Cambridge. The collaboration would result in the publication of Philosophiæ Naturalis Principia Mathematica, the first major work to describe the laws of physics in mathematical terms, despite objections and claims of plagiarism from Robert Hooke and financial difficulties of the Royal Society of London. Tyson explains how this work challenged the prevailing notion that God had planned out the heavens, but would end up influencing many factors of modern life, including space flight. Tyson further describes Halley's contributions including determining Earth's distance to the sun, the motion of stars and predicting the orbit of then-unnamed Halley's Comet using Newton's laws. Tyson contrasts these scientific approaches to understanding the galaxy compared to what earlier civilizations had done, and considers this advancement as mankind's first steps into exploring the universe. The episode ends with an animation of the Milky Way and Andromeda galaxies' merging based on the principles of Newton's laws.