The dome that crowns Florence's great cathedral of Santa Maria del Fiore, the Duomo, is a masterpiece of Renaissance ingenuity and an enduring source of mystery. Still the largest masonry dome on earth, it is taller than the Statue of Liberty and weighs as much as an average cruise ship. Historians and engineers have long debated how its architect, Filippo Brunelleschi, kept the dome perfectly aligned and symmetrical as the sides rose and converged toward the center." More than four million bricks could collapse at any moment -- and we still don't understand how Brunelleschi prevented it. To test the latest theories, a team of U.S. bricklayers will help build an experimental "mini-Duomo" using period tools and techniques.

the final episode deals with plants that live in hostile environments. Attenborough visits Ellesmere Island, north of the Arctic Circle, to demonstrate that even in a place that is unconducive to life, it can be found. Algae and lichens grow in or on rock, and during summer, when the ice melts, flowers are much more apparent. However, they must remain close to the ground to stay out of the chilling wind. In the Tasmanian mountains, plants conserve heat by growing into 'cushions' that act as solar panels, with as many as a million individual shoots grouped together as one. Others, such as the lobelia in Mount Kenya, have a 'fur coat' of dense hairs on their leaves. The saguaro cactus in the Sonoran Desert flourishes because of its ability to retain vast amounts of water, which can't be lost through leaves because it has none. Many desert dwellers benefit from an accelerated life cycle, blooming rapidly within weeks after rainfall. Conversely, Mount Roraima is one of the wettest places on Earth. It is a huge sandstone plateau with high waterfalls and nutrients are continuously washed away, so plants have to adapt their diet if they are to survive. A bladderwort is shown invading a bromeliad. Inhabitants of lakes have other problems to contend with: those that dominate the surface will proliferate, and the Amazon water lily provides an apt illustration. Attenborough ends the series with an entreaty for the conservation of plant species.

Travel back 66 million years to when majestic dinosaurs and extraordinary creatures roamed the lands, seas, and skies in the second season of this acclaimed series narrated by David Attenborough.
After a tropical storm, two Zalmoxes find themselves in a rafting event. On a small island, a monumental display takes place as several Hatzegopteryx ambush a herd of Tethyshadros. A female Majungasaurus hunts a group of Simosuchus. A mother Adalatherium raises her offspring in a burrow, hoping to keep them safe from predators like Masiakasaurus and Madtsoia. A pack of Imperobator pursue a Morrosaurus onto a frozen lake. A male Hatzegopteryx attempts to attract a mate.

Professor Brian Cox takes on the story of the force that sculpts the entire universe - gravity. Gravity seems so familiar, and yet it is one of the strangest and most surprising forces in the universe. Starting with a zero gravity flight, Brian experiences the feeling of total weightlessness, and considers how much of an effect gravity has had on the world around us. But gravity also acts over much greater distances. It is the great orchestrator of the cosmos. It dictates our orbit around the sun, our relationship with the other planets in our solar system, and even the way in which our solar system orbits our galaxy. Yet the paradox of gravity is that it is actually a relatively weak force. Brian takes a face distorting trip in a centrifuge to explain how it is that gravity achieves its great power, before looking at the role it plays in one of the most extraordinary phenomena in the universe - a neutron star. Although it is just a few kilometres across, it is so dense that its gravity is 100, 000 million times as strong as on Earth. Over the centuries our quest to understand gravity has allowed us to understand some of the true wonders of the universe, and Brian reveals that it is scientists' continuing search for answers that inspires his own sense of wonder.

The most famous – and perhaps most misunderstood – episodes in the epic history of the Holy Wars that are known to history as The Crusades – the clash between Richard the Lionheart and Saladin. In July 1192, Richard the Lionheart stood poised for a strike on Jerusalem, while Saladin – mighty sultan of Islam – readied his troops inside the city, preparing for the inevitable attack. During a year-long campaign across Palestine, these two legendary leaders had fought each other to a stand-still. Thousands had perished, appalling atrocities had been perpetrated on both sides. And now they faced each other in a battle for their sacred objective.

Earthflight departs on its grand European tour, using a host of techniques including taking extraordinary footage from microlites as they fly alongside imprinted birds. Among other wonders, cameras soar with cranes and geese over Venice, the white cliffs of Dover and Edinburgh. White storks leave Africa and struggle to reach Istanbul, the gateway to Europe, while cranes take an easier route over the monkey-guarded Rock of Gibraltar. In France, the white horses of the Camargue make a splash around the new arrivals. In Rome, the heat of the city lures 20 million starlings that perform nature's greatest aerial display to outwit peregrines. In Hungary, sand martins grab mayflies from the air; and at Bass Rock, gannets create Britain's greatest natural spectacle as they dive in exquisite slow-motion. The story takes an emotional turn as storks and swallows wait for their partners to return and indulge in a spot of DIY to impress. Finally, geese touch down in Svalbard to raise a family. To protect their young, a squadron of birds assemble to see off polar bears. With views of birds flying over the Loire Valley, London docklands and the bulb fieds of Holland, this is Europe as never before.