Phaethon was born in the palace of Helios, the great golden house that stands at the eastern edge of the world where the sun rises from the Oceanus stream each dawn. His mother was Clymene, one of the three thousand Oceanids, the daughters of Oceanus and Tethys, or in some accounts she was a mortal woman of Ethiopia, a land so close to the sun that its people were dark-skinned from the constant heat. Phaethon grew up in the radiance of his father's house, surrounded by light, and he was proud of his parentage, perhaps too proud for a boy who had never done anything to earn his own glory. When he went to school with the other sons of heroes and gods, the boys mocked him. They said he was not the son of Helios at all, that his mother was a liar, that no god would claim a boy so ordinary. Phaethon burned with shame, and he travelled to the palace of the sun to demand that his father acknowledge him before the whole world.

The palace of Helios was a wonder beyond description. Its columns were of gold, its roof of silver, its floors of polished amber that caught the light and threw it back in a thousand colours. Helios sat upon his throne, wearing a robe woven from the light of the stars, and around him stood the Hours, the goddesses who govern the seasons, and the Seasons themselves, who prepare the chariot each dawn. When Phaethon entered, Helios knew him immediately, for the sun sees everything, and he embraced his son and promised to grant him any wish, swearing by the river Styx, the most terrible and binding oath in the cosmos, the river by which even the gods themselves are bound. Phaethon asked the one thing Helios had hoped he would not ask: he asked to drive the sun chariot across the sky for one day.

Helios tried to dissuade him. The chariot was not a toy, he said. It was drawn by four horses, Pyrois, Eous, Aethon, and Phlegon, whose names mean Fire, Dawn, Blaze, and Flame, and they were wild beyond any mortal's control. The path across the sky was narrow and steep, rising from the eastern Oceanus to the zenith and then plunging toward the western sea, and if the charioteer lost the reins for a moment, the horses would bolt. The earth would burn, the heavens would freeze, and the cosmos would collapse into chaos. But Phaethon was young, and proud, and he held his father to the oath. Helios, bound by the Styx, could not refuse. He placed the crown of burning light upon his son's head, warned him one last time to hold tight to the reins, and watched with a father's dread as the horses leaped from the eastern gate.

The ride began well enough. The horses knew the path, and for the first hours they ran true, pulling the sun across the morning sky. But Phaethon was not strong enough to control them. He was a boy, not a Titan, and the horses felt his weakness. They veered from the track, first rising too high so that the earth below grew cold and the constellations themselves began to smoke, then plunging too low so that the mountains caught fire and the rivers turned to steam. The Sahara was created in that moment, the Libyan desert scorched to sand by the sun's too-close passage. The skin of the Ethiopians darkened from the heat. The ice caps of Scythia melted and then froze again as the chariot rose and fell. The earth cried out to Zeus, the king of the gods, begging him to save the world from destruction.

Zeus answered with a thunderbolt. He struck Phaethon from the chariot, and the boy fell like a falling star, trailing fire across the sky, until he struck the river Eridanus in the far west. The waters closed over him, and the fire was quenched, and the chariot, driverless, was caught by Helios himself, who had leaped into the sky to save what he could. Phaethon's body was buried by the river nymphs, and his tomb was shown to travellers for centuries. But his death was not the end of the tragedy. His sisters, the Heliades, the daughters of Helios and Clymene, wept so inconsolably at his fall that the gods transformed them into poplar trees, and their tears became amber, the golden resin that still drips from poplars into the waters of the Eridanus, which the Romans called the Padus and we call the Po. His friend Cycnus, the king of the Ligurians, mourned him so deeply that he too was transformed, into a swan, and placed among the stars as the constellation Cygnus, the Swan, where he still flies across the Milky Way.