For more than a thousand years, the peoples of ancient Greece consulted oracles for guidance. In political decisions or in the quandaries of daily life, they turned to the gods (usually Apollo), and asked for advice in words. The pilgrimages to Delphi or to Didyma, where questions of political moment received responses in verse from an inspired prophetess, are the best known cases; but there were hundreds of oracles across the Greek world to which private people turned for advice on merely personal questions. At Dodona in northern Greece, many of the questions have survived, inscribed on strips of lead, and they include such trivia (from our perspective) as 'Did Thopion steal the silver?' and 'Would I do better... if I took a wife?' Unfortunately the answers have not survived, but the form of the questions shows that they must have received a yes-or-no answer; and that is not surprising, since we know that the oracles were obtained by lot at this shrine (and at many others).

The simplicity of the expected answers is very revealing about the nature of ancient oracles. The popular picture of a raving prophetess uttering mystical gibberish is very far from the norm. The mythology of Delphi told that the oracular function had been discovered by a goatherd who observed the strange behaviour of his goats when they neared a certain cleft in the rock; so, the story went, they tried the fumes on a local girl and found her hallucinatory mouthings could be interpreted as messages from the gods. The practice became institutionalised, though the people soon turned to using an older woman as they found that a young one attracted the wrong sort of clientele. The story has been dismissed as fantasy, but in recent years geologists have identified a faultline in the rocks at Delphi which could, in the past, have led to emissions of hallucinatory gases; so the Pythia (the prophetess of Apollo) may have been in a trance after all.

The story is puzzling as all the stories we know of about the historical interventions of the Delphic oracle depict a rational functionary who uttered riddling pronouncements in competent hexameter verses. It will not do to say that her ravings were composed into neat form by assistant priests at the shrine, since all sources speak as if the Pythia spoke the verses directly; furthermore, she was sometimes susceptible to bribery (herself, not her colleagues), and when Alexander the Great was refused an oracle because he visited on a 'closed' day, his reaction was to fling the woman to the ground, whereupon she gasped 'Young man, no one can resist you!' - which gave him the pronouncement he wanted.

We shall never know just what took place in the shrine at Delphi. A veil of religious silence was drawn over the precise operation of all such shrines. An inscription from the oracular shrine at Koropi in Thessaly gives very full details about the mode of consultation: you had to wear white clothes, form an orderly queue, behave in a seemly manner, and hand in your petition slip in turn to the officiant, who would place all the slips in an urn which he then sealed and put in the shrine overnight. 'And in the morning, when the god has given his answer.' the inscription continues, skipping over just what we should most like to know, the urn was unsealed and the petitions returned with accompanying answers.

No other oracles besides Delphi relied on ecstatic trances. At Didyma the priestess purified herself in an unspecified manner and then sought inspiration, which is not to be confused with ecstatic trance or hallucination, since she too was capable of immediately composing answers in verse. Something similar seems to have happened at Claros, where the consultant was led via a winding passage into an underground chamber below the temple to hear the (male) priest pronounce his words of doom.

But such grand pronouncements were not the most common form of oracle shrine in the Greek world. At Dodona, as has been mentioned, lots were drawn from an urn. An anecdote in the geographer Strabo tells how one consultation was ruined when the urns were upset by the King of Molossia's pet monkey: so perhaps there were two urns, from which the priests took respectively the question slips and, say, beans, which could be black and white for the two types of answer.

In the second century AD dice oracles became extremely popular in southern Asia Minor. One can still visit a tomb at the coastal city of Olympus near Antalya, where one of the pillars is inscribed with twenty-four lines of verse, one beginning with each letter of the alphabet. When I take visitors there I invite them to choose a letter (perhaps their own initial) and think of a question. The answers take the form 'You will carry off everything successfully; the god says so'; 'Violence is weak if it is not employed in accordance with the laws'; 'It is hard to fight against waves; wait a while'; 'If you work half-heartedly you will reproach the gods later'; 'It is not beneficial to harvest raw fruit'. It is surprising how often my companions say that the answer gives an excellent response to their secret question!

These answers may seem to be no different from fortune cookies drawn from a bran tub. But most of the inscribed dice oracles were presided over by a statue of Hermes, messenger of the gods, who explicitly is there to convey the words of the oracular god Apollo.

A particularly popular form of oracular consultation was by seeking a dream in the shrine of a healing god, Asclepius or Sarapis. The major shrines of Asclepius, at Pergamon or at Aegeae, became something between a sanatorium and a research institute; but scholars have counted over 900 shrines of Asclepius across the classical world, and those of Sarapis became nearly as common. In a dream, the god would appear to the consultant and enjoin some perhaps bizarre activity: the orator Aelius Aristides was once told to scrub his teeth with ground-up lion's tooth, and inscriptions from Epidaurus record cases when the god, in a dream, performed a surgical operation on the patient, who woke up cured.

The oracles came to an abrupt end when the Christian emperor Theodosius abolished all forms of pagan observance in AD 395. For a century before that, Christian philosophers had been debating whether the oracles were the work of fraudulent priests or of genuine, but evil, 'demons'. The debate still continued in the seventeenth century when Anton van Dale wrote his De oraculis veterum ethnicorum (Amsterdam 1700). What is abundantly clear is that, even if the temples were closed, the need for life advice did not come to an end. The anxious now took their questions to the shrines of saints (and later, Muslim holy men); the tomb of a doctor in eighteenth century Naples was a regular place of pilgrimage for the sick. The gods may be dead, but they are indispensable.