Millions of Hindu devotees, mystics and holy men and women from all across India are flocking to the northern city of Prayagraj for the Maha Kumbh Mela festival, touted as the world’s largest religious gathering.

At least 400 million people are expected at the confluence of the three holy rivers – the Ganges, Yamuna, and the mythical, invisible Saraswati – over the next 45 days, according to officials.

A vast ground along the banks of the rivers has been converted into a sprawling tent city equipped with more than 3,000 kitchens and 150,000 restrooms. Divided into 25 sections and spreading over 40 square kilometres (15 square miles), the tent city also has housing, roads, electricity, water, communication towers and 11 hospitals. Murals depicting stories from Hindu scriptures are painted on the city walls.

Indian Railways has also introduced more than 90 special trains that will make nearly 3,300 trips during the festival to transport devotees, besides regular trains.

About 50,000 security personnel are stationed in the city to maintain law and order and for crowd management. More than 2,500 cameras, some powered by AI, will send crowd movement and density information to four central control rooms, where officials can quickly deploy personnel to avoid stampedes.

Over the next six weeks, Hindu pilgrims at the site will take part in elaborate rituals, hoping to begin a journey to achieve Hindu philosophy’s ultimate goal: the release from the cycle of rebirth.

The festival has its roots in a Hindu tradition that says the god Vishnu wrested a golden pitcher containing the nectar of immortality from demons. Hindus believe that a few drops fell in the cities of Prayagraj, Nashik, Ujjain and Haridwar, the four places where the Kumbh festival has been held for centuries.