Water and waterways were vital to the lives of the inhabitants of ancient Greece, and as such they were duly revered. Indeed Poseidon, god of the seas, was one of the most important of all deities in the Greek pantheon. Rivers were also important, and also had a deity associated with them.

The River Styx is probably the most famous of the rivers named in Greek mythology, although it is far from being the most important of them.

Many people will know that the River Styx is to be found in Hades, the underworld of Greek mythology. Ancient sources, including Hesiod and Homer, tell of how the river circles around the underworld nine times.

The River Styx though is only one of the five rivers present in Hades. The River Styx is known as the river of Hate; the River Acheron is the river of woe; the River Cocytus is the river of lamentation; the River Phlegethon is the river of fire, and the River Lethe is the river of forgetfulness. The Rivers Eridanos and Alpheus are also sometimes named as being present in the underworld.

Of these other rivers, Acheron is probably the most important, and is the river over which Charon ferries the dead, and is also the river guarded by Cerberus. It is a common misconception that Charon and Cerberus are both to be found by the River Styx, and indeed some later sources do transfer the mythology of the Acheron across to the Styx.

Like all of the rivers of ancient Greece, the River Styx has its own deity associated with it. The Potomai are the usual male deities associated with rivers but in the case of the Styx, the deity is a female goddess. The goddess Styx was an Oceanid, one of the three thousand daughters of Oceanus and Tehtys. The goddess was honoured by Zeus by being the first to aid the Olympian gods against the Titans during the Titanomachy.

The honour bestowed on the goddess Styx manifested itself by the fact that gods would swear binding oaths upon her name. Any gods who failed to keep their word once they had sworn upon Styx would be forced to drink from the River Styx, resulting in the loss of their voice for nine years.

The power of this oath was exhibited in two tales. Semele, mother of Dionysus, managed to get Zeus to swear on the name of Styx that the supreme god would do whatever she desired. Semele though asked to see Zeus in all his glory to prove his divinity. This though resulted in her death, mortals being unable to look directly on the god.

A second story is told of Phaeton who convinced his father Helios to allow him to ride his sun-chariot for a day, with disastrous results.

Some sources also claim that it was into the River Styx that the demi-god Achilles was dipped to ensure his immortality, although others claim that it was Ambrosia and fire that gave him his invincibility.