Held every 12 years, the Maha Kumbh Mela or Great Pitcher Festival attracts more than 400 million visitors.
It involves a series of ritual baths by Hindu sadhus, or holy men, and other pilgrims at the point where the mythical Saraswati river is believed to meet the Ganges and Yamuna rivers.
The festival is rooted in Hindu mythology, a battle between deities and demons for control of a pitcher containing the nectar of immortality.
Organisers have likened the scale of this year’s festival to that of a temporary country, forecasting up to 400 million pilgrims to visit before the final day on Feb 26.
Mindful of the risk of deadly crowd accidents, police this year installed hundreds of cameras at the festival site and on roads leading to the sprawling encampment, mounted on poles and a fleet of overhead drones.
The surveillance network is fed into a sophisticated command and control centre that is meant to alert staff if sections of the crowd get so concentrated that they pose a safety threat.
More than 400 people died after being trampled or drowned at the Kumbh Mela on a single day of the festival in 1954, one of the largest tolls in a crowd-related disaster globally.
Another 36 people were crushed to death in 2013, the last time the festival was staged in the northern city of Prayagraj.
