They lived in caves in the far west, near the gates of the Underworld. They were sent through one of two gates there. One gate was made of horn, from there the true or prophetic dreams come from. The other gate was made of ivory, from there the false and meaningless dreams come from.
The were shown as black-winged daemons.
The most powerful of the Oneiroi was Morpheus. His brothers Phobetor and Phantasos shape parts of dreams, while Morpheus shapes the dream in general. Morpheus shapes human figures, Phobetor shapes animal figures and Phantasos shapes inanimate objects. Also, Morpheus can cast a layer of magic to put mortals to sleep for a VERY long time. He was a powerful god, even though he was the god of SLEEP!