Though Devtas and Asuras were cousins, then to they were at war with one another very often. In one such war the gods were on the verge of defeat.They were helpless and their forces were dead in large numbers. So they went to Brahma and pleaded for help.
Brahma meditated for a while and then said," Let's take refugee in Lord Vishnu. He always helps those who have faith in him."
Lord Vishnu after listening the whole problem advised them, "You will have to strive hard and obtain the nectar of immortality by churning the ocean and that is the way out for you."
Hearing the advice Indra asked lord Vishnu that how could they churn a Ocean? Vishnu replied, " You must cast all kinds of plants, grasses, herbs & creepers into the ocean of milk.Then churn the ocean using using Mount Mandara as a churn- dasher & Vasuki ( king of serpents) as a rope for turning it."
But one more question arouse that how can the devtas move mount Mandara. Lord Vishnu said, " Take help of Asuras and use them to achieve your end, and REMEMBER you must be careful, however, not to covet any of the things that come out of the ocean and to give vent to anger if any of those things are forcibly taken away by asuras."
"But what about the nectar, if the Asuras took away that also from us then?" asked the devtas. Lord Vishnu assured them that Asuras will not get the nectar. Convinced Brahma returned to his abode while Indra & the devtas went to meet BALI ( King of Asuras).
Seeing Indra unarmed and helpless the Asuras ran towards him but Bali shouted,"No, let's wait.Perhaps the devtas have come with a proposal that might be worth our while." Bali received Indra & the devtas with respect. Indra told Bali about their mission of arrival and requested them ( Asuras) to forget the fight and work altogether to achieve the task.
Bali & His chiefs favored the proposal and peace was declared between them and they ( Asuras) suggested that let's not waste time and begin the task immediately.
Mount Mandara was needed as a churning rod. The strong warriors made efforts with their hordes in uprooting the mountain and carrying it to the ocean. But they barely had covered half the distance and they got tired and the mighty mountain fell, crushing large numbers of Devtas & Asuras under it.Seeing this Indra prayed to Lord Vishnu for his help.
Lord Vishnu came on Garuda ( His mount) to save the Devtas. Lord Vishnu brought the mountain to the ocean with the help of Garuda.When the mountain was placed in the ocean Vasuki came at the scene to play his role. Lord Vishnu addressed him by saying, "Play your role & you shall receive your share of the nectar. The jagged surface of the Mount Mandara will not hurt you at all."
Reassured Vasuki rounded himself around the mountain. The gods held the Vasuki at its mouth's end and the demons at its tail and with full of joyous anticipation Devtas & asuras started churning the ocean.But their joy soon turned into despair, as the heavy Mount Mandara, which had noting to support it, sank into the ocean.
Lifting it out was a great problem. The gods requested Vishnu once again for help and Vishnu said, "Well, I'll take the form of a tortoise and hold the mountain on my back until the ocean is fully churned and nectar is obtained." Vishnu became a tortoise and held the mountain on his back.
As the churning proceeded fourteen magnificent treasures emerged from the ocean* see at the bottom.
The churning began but the Forceful churning first threw up the deadly poison HALAHAL, which was the concentrate of the impurities of the ocean.Its poisonous fumes choked the Devtas & Asuras.
Frightened out their wits few Devtas ran to Lord Shiva at Mount Kailash for help. God assured them that they need not to fear as he will drink the poison. Lord Shiva collected the poison and swallowed it.
Once all the poison was removed from the ocean the devtas & Asuras again began churning the ocean. As they continued churning many precious things rose to the surface, but not the nectar. At last there came out Dhanvantari with a pot of nectar in his hand.
Seeing this the Asuras ran towards Dhanvantari & snatched the pot of nectar from him and their was a great rivalry between the asuras to take possession of the pot of nectar.Devtas watched this in dismay.But remembering Lord Vishnu's command that they should not quarrel over whatever comes out of the ocean, they made no move. Vishnu became very pleased with devtas. He told Devtas," Do not be dejected. The greed of nectar has already divided the Asuras and now I shall charm them with my powers & give you the nectar."
Vishnu took the form of Mohini ( the most beautiful women) and approached the asuras. The asuras forgot about the nectar as they were enamoured by the glances of Mohini. They were prepared to do anything she said. Vishnu, in the form of Mohini, said to them, "You must do as I ask you to do." So infatuated were the Asuras that they entrusted the jar of nectar to her.
Mohini then said to the Asuras that," I will do so if you don't question my actions." Not knowing who she really was they agreed to her proposal. She then instructed ,"Go and take bath & assemble in a row, Asuras in one row & devtas in the other row."
When they had all assembled Mohini began to serve the nectar to the gods first. The demons thought, "Mohini would be displeased unnecessarily if we object to it."
Mohini kept the asuras under her spell and she finished the pot of nectar by giving the whole nectar to the devtas. Then she assumed her original form, The form of Lord Vishnu. Asuras were surprised to see this as they had been deceived and there was no nectar left for the Asuras. After finishing his task Lord Vishnu flew away on his Garuda.
The furious Asuras declared war with the devtas. The Devta- Asura war on the seashore was a terrible one but Devtas who had drank the nectar of immortality fought with the asuras and drove them away.
In this way Lord Vishnu revived the lost glory of those who were gentle and sought refugee in him and punished those who were aggressive and had no faith in him.
Fourteen Teasures that came out of the ocean during churning were:
1) The wish-fulfilling tree Kalpavriksha. The Yakashas began its guardian. Its branch bore every kind of fruit and flowers one wished for.
2) The wish-fulfilling cow Kamadhenu. The sages decided to take care of it. Its udders produced enough food to feed the whole universe.
3) The wish-fulfilling gem Chintamani. Some say Vishnu placed it on his crown. Others say that the Nagas hid it, fact not exactly known.
4) The seven-headed flying horse Ucchaishrava. Bali, leader of the Asuras, took possession of this horse.
5) The six-tusked elephant Airavata. Indra made this beast his mount.
6) The conch of the conqueror Panchajanya. The demon that took possession of it was killed by Vishnu who turned the conch-shell into his trumpet.
7) The bow of the king Saranga. It was given to the kings of earth.
8) The beautiful nymph Rambha. She knew how to pleasure the senses in 64 different ways. She won Indra's heart so he carried her off to Amravati, radiant city of the Devtas.
9) The handsome moon-god, Chandra. Every woman fell in love with him. He cast the spell of romance across the universe.
10) The goddess of wine Varuni. She became the wife of Varuna, the ocean-god, and came to be loved by all creatures.
11) The physician Dhanvantari. An incarnation of Vishnu, the enemy of disease, he brought with him Ayurveda, the science of healing.
12) The goddess of fortune Sri. Everybody wanted to marry her, but she chose Vishnu. She placed Vaijayanti, the garland of eternal victory, around his neck.
13) The elixir of immortality Amrita. The Asuras stole this much-sought-after drink. Vishnu, in the form of the enchantress Mohini, bewitched the demons so that while they admired her beauty, she poured the drink down the throats of the Devtas.
14) The poison Halahal. Nobody wanted this lethal liquid. So Shiva drank it. The poison turned his neck blue.