The Samudra Manthan, the churning of the cosmic ocean of milk, is narrated across the Mahabharata and several major Puranas as a cooperative effort between the gods and the demons, temporarily allied, using the serpent Vasuki as a churning rope wound around Mount Mandara, to extract amrita, the nectar of immortality, along with numerous other treasures and beings that emerged from the ocean during the prolonged churning process, including the goddess Lakshmi and the physician god Dhanvantari, who finally emerged bearing the pot of nectar itself.
A struggle immediately broke out between the gods and demons over possession of the amrita, and Vishnu, taking the form of the enchantress Mohini, distracted the demons and distributed the nectar exclusively to the gods, securing their immortality and the demons' continued exclusion from it. Later tradition, developing beyond the core Mahabharata and early Puranic accounts of the churning itself, holds that during the struggle over the pot, drops of the precious nectar fell to earth at four separate locations, each subsequently sanctified by the spilled nectar's presence.
This later tradition identifies the four sites as Prayagraj, at the confluence of the Ganges and Yamuna rivers, Haridwar, on the Ganges, Ujjain, on the Shipra river, and Nashik, on the Godavari, each of which today hosts the Kumbh Mela pilgrimage festival on a rotating cycle.