For the first time in history, more people live in cities than the countryside. Across the globe, we have 21 cities with more than 10 million people, and these numbers are set to increase - busy, noisy, crowded megacities are the future. In a fascinating three-part series, Andrew Marr finds out how these heaving mega-metropolises feed, protect and move their citizens.

In the first episode, Andrew looks at how people live in five of the world's biggest megacities: London, one of the world's oldest megacities; Dhaka, the world's fastest-growing megacity; Tokyo, the largest megacity on Earth; Mexico City, one of the most dangerous cities in the world; and Shanghai, arguably the financial capital of the world.

Andrew compares the sleek skyscrapers and rapid modernisation of Shanghai to the colourful street culture and geographic sprawl of Mexico City. He spends a night living in a one-room shack in Dhaka's toughest slum, taking his turn to fetch water, cook and clean; and he rents a friend in the efficient and high-tech, but alienating, city of Tokyo.

As he gets under the skin of each unique metropolis, Andrew discovers how the structure of each megacity defines every aspect of its inhabitants' daily lives. And he considers what the megacities of the future can learn from the metropolises of today. Show less