The Maha Kumbh has evolved from bygone era of the universe when demigods and demons conjointly produced the nectar of immortality. It is said that demigods and demons assembled on the shore of the milk ocean that lies in the celestial region of the cosmos. The demigods and the demons made a plan to churn the milk ocean to produce the nectar of immortality. They then agreed to share the nectar equally once it was produced.
For the task of churning the milk ocean, the Mandara Mountain was used as the churning rod, and Vasuki, the king of serpents, became the rope for churning. As the churning began, the Mandara Mountain began to sink deep into the ocean, at which time Vishnu incarnated as a great tortoise and supported the mountain on His back. With the demigods at Vasuki’s tail and the demons at his head, they churned the milk ocean for one thousand years.
The churning of the milk ocean first produced a deadly poison that Shiva drank without being affected. As Shiva drank the poison, a few drops fell from his hands and were locked up by scorpions, snakes, and similar other deadly creatures. After Shiva drank the poison, numerous opulent items were produced. First a Surabhi cow appeared, who could yield unlimited quantities of milk. A white horse named Uccaihsrava was then produced, as well as a white elephant named Airavata. Then a valuable gem called the Kaustubha-mani appeared.
Next came the apsaras, beautiful dancing girls, and a host of other wonderful things appeared from the milk ocean. At last, a male person named Dhanvantari appeared carrying the pot of immortal nectar in His hands. Seeing Dhanvantari with the pot of nectar, both the demigods and demons became anxious.
In the meantime, the Asuras took away the Maha Kumbh (Nectar of immortality). This resulted in battle between demigods and demons for twelve long days and twelve long nights. The period is equivalent to twelve human years and this is the reason behind the Maha Kumbh Mela observance in 12 years.
It is also believed that during the chasing few drops of Amrit fell on the places like Prayagraj, Haridwar, Ujjain, and Nashik, thus Maha Kumbh Mela happens as per the schedule in these holy places. Due to the nectar, these places offer unbelievable and mystical power and located on the embankments of the holiest rivers in India.
Haridwar is located on the Ganges in the Devbhumi Uttarakhand, Prayagraj is at the confluence of Ganga, Yamuna, and Saraswati in Uttar Pradesh, Nashik on the bank of Godavari in Maharashtra and Ujjain the adobe of Mahakal on Sipra river in Madhya Pradesh.