Millions of Hindus have congregated in northern India to celebrate a holy festival known as the Ardh Kumbh Mela.  Anjana Pasricha reports from New Delhi, the 45-day event, is the largest religious gathering in the world.  

Starting early this month, millions of devotees began pouring into one of Hindu religion's most holy spots - the confluence of the Ganges, Yamuna and the mythical Saraswati rivers, in Allahabad city.

These pilgrims are coming to participate in a six-week religious event known as Ardh Kumbh Mela, or "half-pitcher" festival. They include Hindu priests and poor villagers, ordinary folks and rich businessmen. Indian expatriates sometimes return to their native country to take part.

They are drawn here by the Hindu belief that a dip in the waters cleanses away past sins, and grants release from the cycle of birth and death, or reincarnations.     

The crowds on the banks of the Ganges were at their thickest on Friday, deemed by astrologists to be one of the most auspicious days for immersion in the river. Hundreds of naked, ash-smeared ascetics - known as Nagas - led the way in the early morning into the frigid waters, brandishing tridents and sticks. The leaders of Hindu monasteries arrived in elaborate throne-like chairs, pulled by tractors.

By the end of the day, the authorities said, some 10 million people had bathed in the river.

Most of them were simple, ordinary pilgrims who traveled from the far corners of the country.

These men and women describe the dip in the river as a moving experience that gave them great happiness. Some of them say they were filled with devotion as they bathed in the river.

The event is billed as the largest religious gathering in the world.  It is expected to have attracted more than 60 million people by the time it concludes in mid-February.

The logistics required for organizing such an event are staggering. Authorities erect a tent city to house the pilgrims. Thousands of police are deployed to maintain order and guard against stampedes, terrorist attacks, and even clashes between rival Hindu sects, which sometimes compete to be the first to take a dip in the water.   

This year, the authorities also flushed the river with fresh water from upstream canals, after some Hindu priests threatened to boycott the festival because the waters were too polluted.

The Kumbh festival is believed to date back 2,000 years. According to Hindu mythology, the Kumbh Mela marks the victory of gods over demons, in a battle over a pot of nectar that gives immortality. Four drops of nectar fell on four towns including Allahabad. The festival alternate among these four sites.