The Samudra Manthana (Sanskrit: समुद्रमन्थन, lit. churning of the ocean of milk) is one of the best-known episodes in the Hindu philosophy narrated in the Bhagavata Purana, in the Mahabharata and in the Vishnu Purana. The Samudra Manthana explains the origin of Amrita.
Indra, the King of Swarga, while riding on the elephant Airavata, came across Sage Durvasa who offered him a special garland given to him by a nymph. Indra accepted the gift and placed it on the trunk of the elephant as a test to prove that he was not an egoistic deva. The flowers on it had a scent that attracted some bees. Annoyed by the bees Airavata threw the garland on the ground. This enraged the sage as the garland was a dwelling of Sri (fortune) and was to be treated as a prasada or religious offering. Durvasa cursed Indra and all devas to be bereft of all strength, energy, and fortune.
In battles following the incident, the Devas were defeated and the Asuras, led by Bali, gained control over the universe. The Devas sought Lord Vishnu's help, who advised them to treat the Asuras in a diplomatic manner. The Devas formed an alliance with the Asuras to jointly churn the ocean for the nectar of immortality and to share it among themselves. However, Vishnu told the Devas that he would arrange for them alone to obtain the nectar.
The Samudra Manthana process released a number of things from the Ocean of Milk. One of them was the lethal poison known as Halahala. However, in some other variations of the story, the poison escaped from the mouth of the serpent king as the demons and gods churned. This terrified the gods and demons because the poison was so powerful that it could destroy all of creation. In the variation, Lord Indra knew that Vasuki would vomit poisonous flames when twisted and pulled, and therefore advised the Devas to hold the tail end of the snake, without telling them the reason. First, the Devas held the head end of the snake, while the Asuras held the tail end. The Asuras were enraged by this, as the lower part of an animal is impure, or less pure, than the part that contains the head. They insisted on holding the head side of the snake. Lord Indra had an inkling that his reverse psychology would work. The Asuras demanded to hold the head of the snake, while the Devas, taking advice from Lord Indra, agreed to hold its tail. When the mountain was placed in the ocean, it began to sink. Vishnu, in the form of Kurma (lit. turtle), came to their rescue and supported the mountain on his shell. The Asuras were poisoned by fumes emitted by Vasuki. Despite this, the Devas and the Asuras pulled back and forth on the snake's body alternately, causing the mountain to rotate, which in turn churned the ocean.
The Devas then approached Lord Shiva for protection. Shiva consumed the poison to protect the three worlds and which in the process gave a blue hue to his throat. In some versions as Lord Shiva drank the poison, he was suffering intense pain, but could not die, as seen by Parvati, his consort. She immediately places a hand on his throat, stopping the poison to flow any further, and by her Maya stopped it forever. As a result, his throat turned blue and he was henceforth called Neelakantha (the blue-throated one; "neela" = "blue", "kantha" = "throat" in Sanskrit).
All kinds of herbs were cast into the ocean and fourteen Ratnas (gems or treasures) were produced from it and were divided between the Asuras and the Devas. Though usually the Ratnas are enumerated as 14, the list in the scriptures ranges from 9 to 14 Ratnas. According to the quality of the treasures produced, they were accepted by Shiva (because of consuming the poison), Vishnu, Maha Rishi's (for Kamadhenu or Surabhi), which was given by Vishnu, the Devas and the Asuras. There were three categories of Goddesses which emerged from the ocean; most lists include:
Finally, Dhanvantari, the heavenly physician, emerged with a pot containing the amṛta, the heavenly nectar of immortality. Fierce fighting ensued between the Devas and the Asuras for it. To protect it from the Asuras, Garuda took the pot and flew away from the battlefield.
The Devas appealed to Vishnu, who took the form of Mohini and, as a beautiful and enchanting damsel, distracted the Asuras; then, she took the amṛta and distributed it among the Devas, who drank it. An Asura named Svarbhanu disguised himself as a deva and drank some nectar. Due to their luminous nature, the Sun god Surya and the moon god Chandra noticed this disguise. They informed Mohini who before the nectar could pass the Asura's throat, cut off his head with her discus, the Sudarshana Chakra. From that day, his head was called Rahu and his body Ketu, which both later became planets. The story ends with the rejuvenated Devas defeating the Asuras and that's why the eclipse mode of the moon means Rahu swallows moon as his revenge. Although, Rahu only has a head and no body. So the god moon chandra comes out from the throat of Rahu and we see the moon again in sky.
The medieval Hindu theology extends this legend to state that while the Devas were carrying the amṛta away from the Asuras, some drops of the nectar fell at four different places on the Earth: Haridwar, Prayaga (Prayagraj), Trimbak (Nashik), and Ujjain. According to the legend, these places acquired a certain mystical power and spiritual value. A Kumbha Mela is celebrated at these four places every twelve years for this reason. People believe that after bathing there during the Kumbha mela, one can attain moksha.
While several ancient texts, including the various Puranas, mention the Samudra Manthana legend, none of them mentions the spilling of the amṛta at four places. Neither do these texts mention the Kumbha Mela. Therefore, multiple scholars, including R. B. Bhattacharya, D. P. Dubey and Kama Maclean believe that the Samudra Manthana legend has been applied to the Kumbha Mela relatively recently, in order to show scriptural authority for the mela.
This myth has been analyzed comparatively by Georges Dumézil, who dubiously connected it to various hypothetical "Indo-European" myths and even the European medieval legend of the Holy Grail, inventing his own original myth (the "ambrosia cycle", or "cycle of the mead") about a theoretical trickster deity who steals the drink of immortality for mankind but fails in freeing humans from death. Dumézil later abandoned his theory, but the core of the idea was taken up by Jarich Oosten, who posits "similarities" with the Hymiskviða. In this Old Norse poem, beer is prepared for the gods by the Jotunn sea god Ægir, after Thor and Tyr recover a giant kettle Ægir needs to make the beer. Oosten claims the serpent Jörmungandr takes the place of Vasuki, although its role in the story is not at all similar or comparable.