An estimated 30 million Hindu pilgrims undertook a ritual bath at the confluence of the Ganges and Yamuna Rivers at the city of Allahabad in northern India on Sunday.
The Kumbh Mela bathing takes place at 18 locations along the river bank.
The BBC reports a total of 100 million bathers are expected across the 55 days of the festival, which is held every 12 years.
Hindus believe a festival dip at Sangam - where the rivers meet - will cleanse sins and help bring salvation.
This occasion is also a Maha Kumbh Mela, which comes round only once every 144 years.
Military forces and commandos and more than 14,000 policemen were deployed to ensure security on Sunday.
Fourteen hospitals at the Mela grounds have already treated more than 150,000 pilgrims since the opening. Two pilgrims have died.
And at least 18 people died in a stampede at the main railway station serving the festival, as pilgrims headed home.
