The gods were not always immortal and unshakeable. There came a time when a sage's curse left them faded and weak, and the asuras — their ancient rivals — pressed their advantage. The gods turned to Vishnu, who gave them counsel as strange as it was wise: to win amrita, the nectar of immortality, they would have to churn the Kshira Sagara, the cosmic Ocean of Milk. And they could not do it without the help of their enemies.

So a truce was struck. The great mountain Mandara was uprooted to serve as the churning-staff, and Vasuki, king of serpents, agreed to be wound around it as the churning-rope. The devas took one end and the asuras the other, and the long tug-of-war began — the mountain spinning first one way, then the other, raking the depths of the sea.

At once the cosmos pushed back. The unsupported mountain began to plunge into the seabed. Vishnu descended in his second great form, the tortoise Kurma, and bore Mandara upon his back, steadying the axis of the whole endeavor. (In many tellings, Vishnu is present three times over — as Kurma below, as a presence steadying the summit above, and lending strength to the pulling gods.)

Then the ocean began to yield its hidden things, and the very first was not a gift but a horror. A boiling, world-ending poison called halahala (or kalakuta) rose up, its fumes threatening to choke all creation. In the moment of crisis it was Shiva who acted. He gathered the poison and drank it; and his consort Parvati, it is said, pressed his throat so the venom could not pass into his body. It lodged there, staining his throat dark blue — and so Shiva is honored forever as Neelkanth, the blue-throated one, the god who swallows what would destroy the world.

The churning resumed, and now came wonders: the wish-granting cow, the celestial tree, the divine elephant, the goddess Lakshmi rising radiant from the waters to choose Vishnu, the moon, and more — the lists vary from text to text, which is part of the story's living richness. At last came Dhanvantari, the physician of the gods, holding aloft the pot of amrita.

Then the truce shattered. The asuras seized the nectar, and to recover it Vishnu took a fourth form — Mohini, a woman of irresistible beauty. Charmed and trusting, the asuras let her distribute the nectar; she served the gods alone. One asura, Rahu, slipped into the gods' ranks in disguise and tasted it — and was beheaded by Vishnu's discus, his immortal severed head and body becoming Rahu and Ketu, who chase the sun and moon and cause eclipses to this day.