India's pop-up mega city

The Kumbh Mela in Allahabad is everything from a sacred Hindu festival to a medieval fun fair. Victor Mallet spends a day at the festival and questions how the state of Uttar Pradesh is capable of building what researchers have called a pop-up mega city for 80m visitors - with water, food, sanitation and electricity - in just a couple of months, when, for the most part, it is unable to provide basic services in its towns and villages.