Latin, oraculum, from oris, of the mouth) is a term applied in ancient divination to the response of a deity, to the deity responding, or to the place where the response is delivered. The παράδοσις and χρηστήριον of the Greeks were employed with nearly the same latitude of meaning; for they were used both for oracular responses and for the seat of the oracle. The origin of the belief in oracles may no doubt be traced to that desire to penetrate the mysteries of the future so characteristic of man in all stages of his development. And not only were oracular responses sought after as a means of gratifying this universal curiosity; they were also prized for the divine sanction which they lent to the undertakings of men. Jove, as the father and ruler both of gods and men, was, to the mind of a Greek or a Roman, the ultimate source of all divine revelations. But so far was he removed above the little affairs of men, that other lesser deities, and even heroes, had to be employed to transmit his will to earth. The oracles of Zeus were accordingly few, while those of other gods were very numerous.

The most elaborate oracular system of ancient times was to be found among the Greeks. What with Sibylline books, auguries, haruspices, and the like, the Roman did not find it necessary to call in the aid of oracular responses to disclose to him the future. The most celebrated oracles of the former people were those of Apollo. There are on record no fewer than twenty-two oracles at which this deity was consulted. These were Delphi, Abar in Phocis, Ptoon in Thebes, Ismenion in Boeotia, Hysiae in Attica, Tegyra in Boeotia, Eutresis near Leuctra, Orbius in Euboea, the Lyceum at Argos, the Acropolis of Argos, Didyma in Miletus, Claros in Colophon, Grynea among the Myrmidons, Lesbos, Abdera, Delos, Patara in Lycia, Telmessus, Cilicia (two), Hybla in Caria, and Hierai Kome on the River Maeander. Of these oracles to Apollo, by far the most famous was that of Delphi. (For a full account of this celebrated oracle, see the article DELPHI.)

The revelations of Apollo were for the most part given by inspiration, while those of Jupiter were merely signs, which mortals had to interpret as best they could. (For the oracles of Zeus, see Dodona and Olympia.) There was also an oracle to Jupiter Ammon in Libya, which had a considerable reputation (Herod. ii. 29, &c.; also iv. 181).

At Patras in Achaea oracles were given by Demeter or Ceres concerning the recovery or death of the sick. In the centre of the market-place at Pharos, in the same district, stood an altar to Hermes or Mercury, at which that deity was supposed to give responses to questions whispered in his ear. At Charax in Caria, was an oracle of Pluto and Cora, with a cave adjoining, in which sick persons slept and had cures revealed to them in their dreams.

In addition to those oracles of the lesser deities, the Greeks also consulted the oracles of certain heroes of distinction. Such were the oracles of Amphiarous, near Thebes, and at Oropus (Herod. viii. 134); of Amphilocheus at Mallos in Cilicia; of Trophimus at Lebedae in Boeotia (Pausanias ix. 37, &c.); of Chalcas in Daunia; of Asclepius at Epidaurus, and elsewhere; of Hercules at Bura in Achaea; of Pasiphaë at Thalamiae; and of Phrixus in Iberia.

While the Greeks, as a rule, had recourse to oracles to discover the will of the gods, the Romans, on the other hand, trusted more to augury and the Sibylline books, for their knowledge of the future. The only Roman oracles with which we are acquainted were those of Faunus, near the Tibur, and on the Aventine; of Fortuna at Antium, Praeneste, and elsewhere; and of Mars at Tiora Matiena.

Oracular responses were given for the most part in Ionic hexameters, partly because the answers of the deity were thus rendered more venerable, and partly because verse had the advantage of being easily remembered. These oracular verses, however, exhibited occasional metrical defects,—and this even at the oracle of Apollo—which provoked the satirical remark, that the god of verse was sadly deficient in poetical accomplishment himself. To prevent this scandal, it is said that the responses were subsequently given in prose, and in the Doric dialect. These responses, as might naturally be expected, were notorious for their want of meaning, obscurity, or equivocation. Ample latitude was generally given for personal preference in interpreting them, and when they were at all intelligible, they generally displayed such an exquisite ambiguity that it was impossible for mortals to tell what they meant, or for the event to turn out different from some of their possible interpretations. The modes in which these deliverances were given were very various. At Delphi, they were uttered by the Pythia; at Dodona, they issued from a hollow rock; at the oracle of Jupiter Ammon, they were pronounced by the priests, who were very numerous. Painted dice were sometimes employed, as at Bura; and lots, sometimes consisting of lettered sticks of oak, were made use of, as in the case of the Italian oracle of Praeneste. A very frequent mode of oracular communication was through dreams, visions, and preternatural voices.

The Urim and Thummim, and the Bath Kôl of the Jews, are supposed by many to have borne a peculiar resemblance to the heathen oracle. (See Kitto's Cyclopaedia of Biblical Literature.)

It was during the most flourishing period of Grecian history that oracles were held in greatest reverence and esteem. Every enterprise, no matter how private or trifling, had to receive the divine oracular sanction before it could be engaged in. Gradually, however, these mysterious deliverances lost their hold upon the public faith. The sceptical few always secretly ridiculed them as the offspring of subtle, unscrupulous priests. The philosopher smiled at them as a fresh illustration of human folly; and the politician, who held them in secret contempt, yet regarded them with public favour as a means of advancing his own designs. (See Cicero, De Divinatione.) "On what account, Labienus," says Cato, in that celebrated passage of Lucan's Pharsalia, lib. ix., "would you have me consult Jove?... Let us not ask him to repeat to us what he has sufficiently written on our hearts. Truth hath not retired into these deserts; it is not recorded on the sands of Libya. Let the irresolute and unstable have recourse to oracles; for my part, I can extract the most steadfast resolution from everything in nature. Death comes to the coward as well as the brave. Jupiter can tell us no more."

While some have believed in the genuine divinity of oracular responses, and others have scouted them as the inventions of designing men, a third party have attributed them to the influence of the devil. The latter view was entertained by the Christian fathers; the second is maintained by Hüllmann (Würdigung des Delphischen Orakels, Bonn, 1837), at the present day; while the first finds a partial advocate in Klausen. (See art. "Orakel" in Ersch and Gruber's Encyclopädie.) Much controversy has also been created respecting the period at which oracles ceased altogether to give forth their deliverances. Eusebius advanced the opinion, and the majority of Christian writers have followed him, that all oracles became silent at the birth of Christ. Milton has adopted this view in his grand Hymn of the Nativity. But traces remain of their having been consulted as late as 358 A.D.; and edicts are known to have been issued against them by the emperors Theodosius, Gratian, and Valentinian. Oracles had long before lost their hold on the public, however, and what faint traces of the superstition still lurked in remote corners gradually disappeared before the superior light of Christianity.

(On the general subject of Greek and Roman oracles, see Wachsmuth, Hellen. Alt., vol. ii.; Hartung, Die Relig. der Römer; Niebuhr's History of Rome; and the Encyclopédie Moderne. Also the works of Daniel Clusens (1673), Anton Van Dale (1683), E. Dickinson (1686), Fontenelle (1687), J. C. Bulenger (1699), and Clavier (1819). On the Delphic oracle, see the works of C. F. Wilzer, Piotrowski, and W. Götte; also those of Hüllmann and Klausen, already referred to. On the oracle at Dodona, see the works of Cordes, Arneth, and Laisaulex.)