The Background
Dakṣa Prajāpati — one of Brahmā's mind-born sons and a presiding lord of creation — had a daughter named Satī (also called Dakṣāyaṇī). Despite Dakṣa's opposition — he considered Śiva an uncouth ascetic unsuitable for his refined family — Satī's devotion to Śiva was absolute. They married. Dakṣa's hostility toward Śiva never abated.
The Great Yajna
Dakṣa organized a grand Bṛhaspati-Sava yajña (a great Vedic sacrifice) and invited all the gods, sages, and notable beings — deliberately excluding Śiva and Satī. Satī, hearing of the sacrifice, insisted on attending despite Śiva's reluctance. Śiva tried to stop her, recounting the insult this would be, but Satī — driven by the desire to see her family — went.
At the sacrifice, Dakṣa publicly humiliated Śiva with vile insults in front of the assembly. Satī, unable to bear the dishonor to her husband, resolved to end her life. In the sacred fire (yogāgni), she immolated herself through yogic power.
Śiva's Grief and Vīrabhadra's Fury
When news reached Śiva, his grief was beyond measure. He took Satī's charred body on his shoulder and wandered the cosmos in anguish performing the Tāṇḍava — a fearful dance of grief and fury. The very stability of the universe was threatened.
From his matted hair (or from a lock he pulled in grief), Śiva created Vīrabhadra — a being of terrible power — and sent him with an army to destroy Dakṣa's sacrifice. Vīrabhadra decapitated Dakṣa, tore out Indra's teeth, cut off Bhaga's eyes, and wreaked havoc. Other accounts mention that Śiva himself arrived and destroyed the yajna. Brahmā, Viṣṇu, and other gods interceded. Śiva relented. Dakṣa was restored to life with a goat's head (his original head had been thrown into the yajna fire). The disrupted sacrifice was completed in altered form.
Viṣṇu's Sudarśana Chakra & The 51 Śakti Pīṭhas
Śiva, still carrying Satī's body, could not be consoled. To free him from grief and protect cosmic order, Viṣṇu deployed his Sudarśana Chakra (discus). As Śiva wandered, the Chakra cut Satī's body into pieces. Various accounts give 51, 64, or 108 pieces — the most common is 51.
Wherever a body-part of Satī fell, a sacred Śakti Pīṭha (power seat of the Goddess) arose. These are among the most sacred pilgrimage sites in the Hindu tradition:
Kamarupa (Guwahati) — Satī's yoni; Kāmākhyā Devī — most powerful of all pīṭhas
Vārāṇasī — Satī's earrings fell here; Viśālākṣī Devī
Kolkata — Satī's right toe; Kālikā / Kālīghāṭa Devī
Vaidhyanāth (Jharkhand) — Satī's heart; Jayā Devī
Nāinādevī (Himachal) — Satī's eyes; Nainā Devī
51 Pīṭhas total — spanning India, Nepal, Bangladesh, Pakistan, Tibet, Sri Lanka
The Rebirth of Satī as Pārvatī
Satī reincarnated as Pārvatī, daughter of the mountain king Himavat and Menā. Her name means "daughter of the mountain" (Parvata = mountain). This sets the stage for the next great Śaiva event — the birth of Skanda.