Kumbh Mela is a mass Hindu pilgrimage. Kumbh Mela is believed to be the largest religious gathering on earth which is held on the banks of the 'Sangam'- the confluence of the holy rivers Ganga, Yamuna and the mythical Saraswati.
It occurs four times every twelve years and rotates among the four locations Prayag (Allahabad), Haridwar, Ujjain and Nashik. Kumbh Mela is practically held every three years across the four locations. The one celebrated at the Holy Sangam in Allahabad is the largest and holiest of them.
There is no precise method of ascertaining the number of pilgrims, and the estimates of the number of pilgrims bathing on the most auspicious day may vary.
What the history says
It is believed that its origin is found in one of the popular creation myths and the Hindu theory, the Samudra manthan episode (Churning of the ocean of milk), which is mentioned in the Srimad Bhagavatam, Vishnu Purana,e Mahabharata and in the Ramayana.
According to the Hindu mythology when the Gods lost their strength they thought of churning the Ksheera Sagara (primordial ocean of milk) for amrit (the nectar of immortality) to regain their lost strength. But it was not enough for Gods to do it themselves so they made a temporary agreement with their enemies (demons or Asuras) to work together, with a promise of sharing the nectar equally thereafter.
After a long period of time when the Kumbha (urn) appeared containing the amrit, a fight started between Asuras and Gods in the sky. It is believed that this fight went for twelve days and twelve nights which is expected to be equivalent to twelve human years.
During this fight which was taking place up above in the sky, the celestial bird, Garuda the vehicle of Vishnu flew away with the Kumbha (urn) and that is when drops of amrita fell at four places on earth: Prayag, Haridwar, Ujjain and Nashik, and that is where the Kumbh Mela is observed every twelve years.
The Kumbh places
Allahabad also called Prayag is at the confluence of the holy rivers Ganga, Yamuna and mythical Saraswati river in Uttarpradesh State.
Haridwar, along Ganga river is in Uttarakahand State.
Ujjain, along the Kshipra river is in Madhya Pradesh State.
Nashik is along the Godavari river is in Maharashtra State.
The Ardh Kumb mela
The Ardh Kumbh mela is celebrated every six years at Haridwar and Allahabad.
The Purna (complete) Kumbh Mela
The Purna (complete) Kumbh always takes place at Allahabad every twelve years.
The Maha Kumbh mela (Great' Kumbh Mela)
The Maha Kumbh Mela, Great Kumbh Mela, is held in Allahabad and comes after 12 'Purna Kumbh Melas' which is after every 144 years.