According to Apollonius of Rhodes and Ovid, amber originated from the tears of the Heliades, encased in poplars as dryads, shed when their brother, Phaethon, died and fell from the sky, struck by Zeus' thunderbolt, and tumbled into the Eridanos, where "to this very day the marsh exhales a heavy vapour which rises from his smouldering wound; no bird can stretch out its fragile wings to fly over that water, but in mid-flight it falls dead in the flames"; "along the green banks of the river Eridanos," Cygnus mourned him—Ovid told—and was transformed into a swan.