The Hoover Dam in the US, the Aswan Dam in Egypt and the recently opened, and sumptuously named, Grand Ethiopian Renaissance dam. Since modern times, huge mega dams like these to tame rivers, create water storage and hydropower, have become a symbol of nationhood used to create national pride and bolster political power, from the Cold War to today. Nehru, the first Prime Minister of India, called dams the temples of modern India. But dams have also been highly controversial, displacing rural populations, disrupting local ecology and more recently it’s been shown that dams can increase the amount of greenhouse gases in the earth’s atmosphere. So why are so many countries like China still highly involved in dam building, and will they need to change tack in the future? And, could the humble beaver offer a solution? To discuss the past, present, and future of dam building, Rajan Datar is joined by Nikita Sud, Professor of the Politics of Development at Oxford University; Donald C. Jackson the Cornelia F. Hugel Professor of History at La Fayette University in the US and author of many books on the history of dam building, including Building the Ultimate Dam: John S. Eastwood and the Control of Water in the West; and Dr Majed Akhter, a political geographer who is senior lecturer in Geography at King’s College London. With the contribution of Dr Emily Fairfax, an ecohydrologist with an expertise in beaver activity and beaver dams from California State university Channel Islands in the US. Produced by Anne Khazam for the BBC World Service. (Photo: The Hoover Dam on the Colorado River straddling Nevada and Arizona at dawn. Credit: Sean Pavone via Getty Images)

From Persia to India to Greece – they called him The Great – that is Alexander the Great. Also known as Alexander III of Macedon, he was one of the most successful military leaders of all time. Undefeated by the time of his death in 323 BCE, he is still a go-to figure when people want to define an empire builder. But how should we view this often cruel and destructive militarist today in the light of current world events? And, despite his brutality, like his ransacking of the beautiful capital city of Persepolis, is there a more progressive side to Alexander, his desire for cultural assimilation for instance, that explains why he became an inspiration not just to nationalists and imperialists but also to writers, poets, and the gay community? To discuss the relevance of Alexander the Great today, Rana Mitter is joined by James Romm, Professor of Classics at Bard College in New York state whose latest book is Demetrius: Sacker of Cities, the failed but would-be successor to Alexander the Great; Dr Haila Manteghi from the University of Münster in Germany who’s the author of Alexander the Great in the Persian tradition; Ali Ansari, Professor of Iranian History at the University of St Andrews in the UK; and Meg Finlayson, a specialist on the evolution of the queer Alexander, from the University of Durham in the UK. Produced by Anne Khazam for the BBC World Service. (Photo: The Alexander mosaic, a Roman floor mosaic from Pompei that dates from circa 100 BCE. Credit: Simone Crespiatico via Getty images)

From coronations to cup finals, many of us love a big event, a ceremony with age-old observances. Indeed rituals, whether public spectaculars or more personal ones, such as a particular daily routine, have been part of human experience since time began. But why do rituals persist even though so many of them seem to serve no obvious practical purpose? Rajan Datar looks for clues in our past with the help of Egyptologist Dr. Elizabeth Frood and historian of Venice Prof. Edward Muir. It turns out that non-human animals – for instance elephants - also display ritual-like behaviour and not always for practical reasons. We hear from a leading behavioural ecologist, Dr. Caitlin O’Connell-Rodwell. We examine whether rituals really do remain unchanging through time: it might seem to be their essential characteristic but in reality they continuously evolve. And what about the power of contemporary collective ceremonies and the strong emotions that swell inside us from being part of a huge crowd? Anthropologist Dr. Dimitris Xygalatas gives us his insights. (Photo: Shinto priests conduct the Oharae ritual in Tokyo. Credit: Tomohiro Ohsumi/Getty Images)

Drawing on traditional music, pop culture, kitsch, rock and modernist poetry to mention just a few of their sources of inspiration, the short-lived Tropicália movement in late 1960s Brazil was provocative and anti-authoritarian. Perhaps most importantly it represented a uniquely Brazilian aesthetic that could only have emerged from that country’s specific culture and history. The movement’s leading lights were eventually arrested by the military regime that governed Brazil at the time, and exiled to London. But Tropicália paved the way for other performers to demand artistic freedom. With the help of musical examples, Rajan Datar and guests will explore what made Tropicália so disruptive. Joining Rajan will be singer Mônica Vasçoncelos and guitarist Gui Tavares, social scientist Professor Liv Sovik from the Federal University of Rio de Janeiro, who’s published widely on Tropicália, including a collection of essays entitled Tropicália Rex: Popular music and Brazilian culture; and David Treece, Emeritus professor of Portuguese at King’s College, London, who’s written extensively on Brazilian popular music, including the book Brazilian Jive: From Samba to Bossa and Rap. Produced by Fiona Clampin for the BBC World Service (Image: Gilberto Gil in The Unique Concert at The Reunion in France. Credit: IMAZ PRESS/Gamma-Rapho via Getty Images)

Nearly everything we consume is transported by ship. The biggest container ships in the world are among the largest moving structures made by man and can carry over 24,000 20-foot container units. The standardisation of these simple metal containers in the 1950s and 60s marked a turning point in world trade, driving down costs and ultimately fuelling globalisation. Now that supply chains have become ever more complex and been put under increasing strain, we take a look at the history of the shipping container. Joining Rajan Datar are Marc Levinson, American historian and economist and author of The Box: How the Shipping Container Made the World Smaller and the World Economy Bigger; Alan McKinnon, professor of Logistics at Kühne Logistics University in Hamburg and author of Decarbonising Logistics: Distributing Goods in a Low Carbon World; Yash Gupta, shipping industry expert with over 20 years’ experience in vessel management and logistics. Presenter: Rajan Datar Producer: Jo Impey for BBC World Service (Photo: Aerial view of a container ship passing under a suspension bridge with truck crossing above. Credit: Shaul/Getty Images)