Making teeming masses predictable

Once every three years, millions of Hindus gather for the Kumbh Mela, the biggest religious festival in the world. This spring, 60 to 80 million pilgrims travelled to the banks of the Shipra river, at the holy city of Ujjain, in central India. On the busiest days, as many as 60 million people were moving around the festival site, which covers an area of thirty square kilometres.