Kumbh Melais a mass Hindu pilgrimage in which Hindus gather at the meeting place, of the rivers Ganges, Yamuna and mythical Sarasvati, at Prayag where bathing for purification from sin is considered especially auspicious.
The festival is billed as the biggest human gathering in the world. In 2001, more than 40 million people gathered on the main bathing day at Allahabad, breaking a world record for the biggest human gathering.
The Ardh (half) Kumbh Mela is celebrated every six years, the Purna or complete Kumbh takes place every twelve years and Maha or the great Kumbh Mela which comes after 12 'Purna Kumbh Melas', or 144 years, is held at Allahabad.
This yearalmost a million Hindu holy men and pilgrims took a bracing plunge in India's sacred Ganges river to wash away lifetimes of sins on Monday, in a raucous start to an ever-growing religious gathering that is already the world's largest.
Officials believe that over the next two months as many as 100 million people will pass through the temporary city making it larger even than previous festivals.
The ritual "Royal Bath" was timed to match an auspicious planetary alignment, when believers say spiritual energy flows to earth.
More than 2,000 years old, the festival is a meeting point for the Hindu sadhus, some who live in forests or Himalayan caves, and who belong to dozens of inter-related congregations. The sects have their own administration and elect leaders, but are also known for violent clashes with each other.
Some naked, some wrapped in saffron or leopard-print cloth and smoking cannabis pipes, the holy men hold court by fire pits in sprawling camps decorated with coloured neon lights, where they are visited by pilgrims who proffer alms and get blessings.
Here are a few glimpses: