Hestia is the goddess of the hearth, the fire burning at the centre of the home around which the family gathers. She is the gentlest and calmest of the gods: she takes no part in quarrels and wars and has hardly any myths. Yet she was deeply revered, because the hearth fire was the heart of every home and every city. To the Romans she was Vesta.
The firstborn
Hestia was the first child of Cronus and Rhea, and so the first to be swallowed by her father and the last to be disgorged: she was therefore considered both the eldest and the youngest of the gods. Courted by Poseidon and Apollo, she swore on Zeus's head to remain a maiden forever. Zeus allowed her to sit at the centre of the house and receive the first share of every sacrifice.
The seat given to Dionysus
According to a late tradition, when Dionysus arrived on Olympus, Hestia gave him her seat among the twelve, preferring to stay by the fire. That is why many lists of the twelve gods include Dionysus in her place.
Her cult
Every Greek family honoured Hestia at its own hearth, and meals began with a small offering to her. Every city had a public hearth in the prytaneum, the building where magistrates met and ambassadors were received: its fire must never go out. When Greeks founded a colony, they carried fire from the mother city's prytaneum to light the new city's hearth. In Rome the cult of Vesta was entrusted to the Vestal Virgins, priestesses who tended the sacred fire in the round temple in the Forum.
See also religion in ancient Greece.