How Did the Oracle at Delphi Work? A Woman, a Question and a Gap in the Rock

The procedure was formal and well documented, though the details varied over the centuries:

• •Consultations were available only on fixed days, initially one a year and later roughly monthly, excluding winter months when Apollo was said to be absent
• •A queue was determined by a system of precedence, with a privilege called promanteia granting the right to consult first, which was granted to individuals and cities as a diplomatic honour and was worth a great deal
• •A goat was sprinkled with cold water and had to shudder before the ritual could proceed, which functioned as a test of whether the god was willing on that day
• •The enquirer paid a fee and made a sacrifice, then put the question, usually by way of the priests
• •The Pythia, the priestess, sat on a tripod in the inner chamber, reportedly holding laurel and a dish of water, and responded in a state described by ancient sources as inspired
• •Her response was conveyed to the enquirer, with ancient accounts differing on whether the priests rendered it into verse or whether she spoke in hexameter herself

Ancient writers, including Plutarch, who served as a priest at Delphi, described a sweet-smelling exhalation rising from the ground in the inner chamber and connected it to the priestess's altered state. Nineteenth-century excavation found no chasm and the account was dismissed as legend for most of the twentieth century. Geological work published from 2001 by a team including a geologist, an archaeologist, a chemist and a toxicologist re-examined the site and reported two intersecting faults beneath the temple, bituminous limestone capable of releasing hydrocarbon gases when heated by fault movement, and traces of ethylene, methane and ethane in spring water and travertine deposits at the site. Ethylene is a sweet-smelling gas used historically as an anaesthetic which at low concentration produces euphoria and altered consciousness without loss of awareness. The finding is contested, with critics arguing that the measured concentrations are too low and the geology differently interpretable, and the debate has not closed. What is agreed is that the ancient accounts of a vapour are no longer simply dismissible.

The oracle's most famous characteristic is answers that could be read two ways, and the celebrated cases show the pattern. Croesus of Lydia was told that if he attacked Persia he would destroy a great empire, did so, and destroyed his own. The Athenians before the Persian invasion were told to trust in wooden walls, which Themistocles interpreted as the fleet, an interpretation that decided Athenian strategy at Salamis. Readings of this vary. The cynical view treats the ambiguity as institutional self-protection, since an oracle that is never demonstrably wrong retains authority indefinitely. A more interesting reading, developed by historians of the institution, notes that most recorded consultations were not predictions at all but questions of the form should we do this, to which the answer was a sanction or a refusal, and that the oracle functioned as a mechanism for legitimating decisions that had already been substantially made. That is a genuine political service: a colony founded with Apollo's approval, or a law issued with it, carried an authority that a purely human decision did not.

Delphi was regarded as the centre of the world, marked by a stone called the omphalos, the navel, and the sanctuary accumulated extraordinary wealth in the form of treasuries built by individual cities to house their dedications, alongside statues and offerings. It hosted the Pythian Games, second only to the Olympics, and was administered by an association of neighbouring states, whose disputes over control produced several sacred wars. Its authority made it a target: it was plundered repeatedly, by the Phocians in the fourth century BCE, by Sulla, and by Nero, who is said to have removed hundreds of statues. Decline followed the decline of the independent Greek city, since an institution for legitimating collective decisions matters less when those decisions are made in Rome. The oracle was finally closed under the Christian emperor Theodosius at the end of the fourth century CE, with a late tradition preserving a final response reporting that the god's hall had fallen and the speaking spring had ceased.

Delphi operated on fixed days, with a paid fee, a sacrifice and a goat whose shudder confirmed the god was willing, after which the Pythia responded from a tripod in the inner chamber. Ancient accounts of an intoxicating vapour were dismissed for a century and revived by geological work reporting fault-derived hydrocarbon gases, a finding still disputed. Most consultations asked whether to act rather than what would happen, which made the oracle a device for legitimating decisions. It closed under Theodosius in the late fourth century.