Supermassive black holes are the engines that power our universe and one of the major players in the evolution of galaxies. They're in fact the driving force at the heart of nearly every galaxy in the cosmos. Now, a new mystery has emerged about the oldest supermassive black holes. We see supermassive black holes in the very early universe. And we don't understand how they grew so large so quickly. We have clues about their formation but, can we solve the mystery of this supermassive growth spurt?

Feast your eyes on a reconstruction of the mega-city and its amazing buildings. Alexandria, built in the middle of rancid marshland, had become in less than a century, the greatest city of the Mediterranean. An ideal position at the crossroads of east and west, and one that brought her great riches. Huge, modern, gleaming white and cosmopolitan, like no other in antiquity, it created its own identity.
While the beauty of its planning, its great arteries, its temples and its ports would be equalled only by its openness to the rest of the world. And the monumental achievements of its sovereigns, still shrouded in mystery, we'll never cease to fire our imagination for millennia to come.

The last episode explores Mescaline, the psychoactive molecule in San Pedro and peyote cacti, a sacred medicine that Native Americans have had to fight for the right to use. At the Indigenous practices there's always an elder, someone who knows the territory very well, who's presiding. There's usually a group, a community is involved, There's always an intention, a purpose to what you're doing, and you're treating it as sacred, in order to achieve altered states of consciousness, which contribute to worship in various ways, or celebration or healing.
But maybe all this is not so new to Western culture after all. In the old Greek histories of Eleusis, people who were initiated there got the drink, the kykeon, and then they had the illumination. The precise recipe is a mystery, but we know that the kykeon was a psychoactive brew that was used at the Eleusinian mysteries, a sacred annual ritual of enlightenment practiced by some of the world's greatest minds including Socrates, Plato, and Aristotle. So why did this ritual come to an end more than 1,000 years ago? Was the possibility of illumination or achieving a higher consciousness considered threatening to the powers that be? Have the drug wars been merely an extension of that fear?
Psychedelics has a major part in how we can heal as a community, how we can heal as a city, and how we can heal as a country. The current renaissance of psychedelics could not come at a better time as the world confronts a crisis in mental health. But psychedelics have much to offer. The psychedelic experience changes the mind in ways that will help scientists better understand how it works. All these altered states allow us to probe what is the greatest mystery in all of nature. The emergence from mere matter of something as miraculous as consciousness. But an even bigger question is whether psychedelics might help us address the environmental crisis of how we think about our place in nature. One of the greatest gifts of psychedelics is how they reanimate the natural world, allowing us to perceive the subject, the spirit of all species, not just our own. And to feel a deeper sense of interconnectedness with nature.

The unearthing of a gruesome grave filled with thousands of skeletons at the beach of Kamakura in Japan could be about to unlock the true extent of the merciless violence and mystery surrounding the true origins of one of the most feared and revered warriors of all time: the Samurai.
In the Middle Ages, Kamakura was the capital of Japan. The 'Shogun', a kind of aristocratic military dictator, ruled here. This shogunate ended in 1333 with the Battle of Kamakura. A drastic event in Japanese history, because this resulted in not only political, but also social, philosophical and technical innovations. The remains of the samurai warriors who fell near Kamakura now provide scientists with detailed insights into the time of the Kamakura shogunate and the bloody conflict between the shogun and the emperor.
The chilling burial ground dates back to 1333. Kamakura was one of the most heavily fortified regions of Japan. When the Emperor became angered by the growing powers of the ruling Hojo family, he sought to retake control of the region, setting the stage for a war that would change the shape of the nation. Among over 4000 sets of remains, six have a unique story to tell: the husband and wife involved in a sword fight to the death; the warrior monk; a peasant boy soldier; and members of the ruling Hojo family, captured and decapitated, with their heads displayed as trophies of victory. These remains reveal the secrets of the Samurai, their ferocious fighting skills and their merciless killing techniques.

Sir David Attenborough explores the surprisingly vibrant seas that surround the British Isles. The vast watery wilderness around us is over three times the size of our land mass, and yet to many, our oceans remain a mystery. Full of colour and teeming with life, the seas of Britain and Ireland are crucially important to a range of wildlife. This episode goes beneath the waves to uncover the thriving habitats that exist along our 22,000-mile coastline.
In winter, clear evidence of the ocean’s abundance can be seen on a beach in Norfolk. Thousands of grey seals congregate on the shoreline to give birth. Britain and Ireland are home to 40 per cent of the world’s grey seals, and the number being born on our shore rises every year. Once the newly born pups are weaned, the females are ready to breed again, and heavyweight males enter violent, bloody fights to win a stretch of beach, and the females along with it.
Beyond the beach, the vibrant shallows contain several important habitats. Rich beds of seagrass are nurseries for a range of animals, while also acting as very important carbon storage areas. They are also home to one of the strangest fish in our waters, the seahorse. We follow a male and female as they perform a balletic mating dance in the water, delicately entwining their tails. The stakes are high, as these animals mate for life.
In a touching piece to camera, Sir David bids a fledging Manx shearwater chick farewell as it embarks on a 6,000-mile journey across the oceans to South America. There is no better example of how important the British Isles and its abundant seas are to the survival of wildlife worldwide.