The Styx was one of the rivers of Hades – the tenth part of the waters of Oceanus – flowing round it seven times with dark and sluggish stream, across which Charon ferries the shades of the departed. The nymph of this stream was the daughter of Oceanus and Tethys, and she first, together with her children, came to the help of Zeus against the Titans. For this service they were taken to Olympus, and she herself became the goddess by whom the most solemn oaths of the immortals were sworn. When such an oath was taken Iris brought some of her sacred water in a golden cup, and anyone who swore falsely by it lay speechless and breathless for a year, and was banished from the councils of the gods.
A rocky stream falling into the Crathis in the north-east of Arcadia bore this name, the scenery around it being fittingly weird and desolate.