At the height of the Greek civilization, in the 5th and 6th centuries BC, many of the shrines to the Gods had a priest (or more likely priestess) who was a channel for divine advice. The shrines were in effect Greek churches, where individuals came to consult their divinity. The responses were always ambiguous, so that if events did not turn out as predicted it was not an error of the Gods. The most famous oracle was at the shrine to Apollo at Delphi, which was consulted from all over the Mediterranean world and thus became the centre of a world-wide intelligence network. Its priests had mastered the art of the ambiguous. By Roman times the oracles were no longer shrines so much as messages from the gods: the Romans based their Prophecies on the Sibylline Books (> Sibyl), but their and other cultures developed a whole industry of augurs, divinators and prophets who claimed Precognition and would utter an oracle for the relevant fee.
Oracles, in the widest sense, feature frequently in fantastic fiction, but in the strict form of ancient Greece they are clearly limited to Fantasies of History or to Heroic Fantasy drawing upon historical sources. They are best represented in the classical fantasies of Thomas Burnett Swann and similar stories evoking Myths and Legends. The most famous Greek prophetess was Cassandra, daughter of King Priam of Troy: given the gift of prophecy by Apollo after she refused to meet his demands, her Curse was that no one would believe her. Cassandra's plight has fascinated many; she is the subject of The Firebrand (1987) by Marion Zimmer Bradley and Cassandra: Princess of Troy (1994) by Hilary Bailey (1936- ). [MA]