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.

Nearly 15 million Hindus, six times the number expected, took a dip in freezing waters seeking absolution of their sins on Monday, the first day of India's festival that could draw the world's largest single gathering of humanity.

Over the coming 45 days, an estimated 400 million Hindus are expected to come together for Maha Kumbh Mela. The festival is held every 12 years but the "Maha" or grand Kumbh Mela takes place only every 144 years, "marking the 12th Kumbh Mela and a special celestial alignment of the sun, moon and Jupiter", said The Guardian.