STYX, in Greek mythology, a river which flowed seven times round the world of the dead. In the Iliad it is the only river of the underworld; in the Odyssey it is coupled with Cocytus and Pyriphlegethon, which flow into the chief river Acheron. Hesiod says that Styx was a daughter of Ocean, and that, when Zeus summoned the gods to Olympus to help him to fight the Titans, Styx was the first to come and her children with her; hence as a reward Zeus ordained that the most solemn oath of the gods should be by her and that her children (Emulation, Victory, Power and Force) should always live with him. Again, Hesiod tells us that if any god, after pouring a libation of the water of Styx, forswore himself, he had to lie in a trance for a year without speaking or breathing, and that for nine years afterwards he was excluded from the society of the gods. In historical times the Styx was identified with a lofty waterfall near Nonacris in Arcadia. Pausanias (viii. 17, 6) describes the cliff over which the water falls as the highest he had ever seen, and indeed the fall is the highest in Greece. The ancients regarded the water as poisonous, and thought that it possessed the power of breaking or dissolving vessels of every material, with the exception of the hoof of a horse or a mule. Considering the undoubted importance attached by the ancients to an oath by the water of the Styx (cf. Herodotus vi. 74), and the supposed fatal result of breaking it, it is probable that drinking the water originally formed a necessary part of the oath, and that we have to do with the tradition of an ancient poison ordeal, common amongst barbarous peoples (for the geography and similar ceremonies see Frazer's Pausanias, iv., pp. 250-255). The people in the neighbourhood, who call it Mavro Nero (the Black Water), still think that it is unwholesome, and that no vessel will hold it.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)