It’s late evening in the city of Prayagraj and the roadside vendors selling snacks are packing up their wares to shut for the night.

A little farther, Nagavalli Gupta reads a prayer book while her husband sits cross-legged wearing a woolen cap, wrapped in a blanket. They are from Bengaluru in the southern state of Karnataka and have been on a pilgrimage for the past two months.

India's Maha Kumbh Mela, or Great Pitcher Festival, is set to be the world's largest gathering of humanity, with 400 million visitors expected at the six-week event that began this week in the northern city of Prayagraj.