People have long been fascinated with the Delphic Oracle and the source of the Pythia’s (priestess) prophetic inspiration. For believers in the oracle, it was an examination of divine inspiration and the means by which the Pythia could communicate with Apollo. For non-believers, this question has been a way of discrediting her and exposing the perceived “con” in her work. Modern writers fit within this second group; they pursue a “rational explanation” to what appears irrational.

The common perception of these oracular prophecies is that they were frantic, erratic, likened to a madness in which the Pythia spoke with a frenzied manner, and so non-divine explanations have been sought. The most prolific in the modern day is the idea that she was inhaling fumes and thus in an intoxicated state when delivering the prophecy. This would explain the erratic, frenzied behaviour, and why she would speak garbled nonsense. This answer is not a uniquely modern one, ancient sources suggested similarly (Strabo 9.3.5):

The place where the oracle is delivered, is said to be a deep hollow cavern, the entrance to which is not very wide. From it rises up an exhalation which inspires a divine frenzy.

Strabo describes two common features of this model, the deep cavern or chasm next to the Pythia, and the presence of air or gas: the Greek word is pneuma, so it may also suggest breath or even spirit. The presence of the hollow suggests that pneuma may refer to a gas coming from underground.

In fact, there was an origin myth about the oracle which corroborates this idea (Diodorus 16.26):

There is a chasm at this place where now is situated what is known as the “forbidden” sanctuary, and as goats had been wont to feed about this because Delphi had not as yet been settled, invariably any goat that approached the chasm and peered into it would leap about in an extraordinary fashion and utter a sound quite different from what it was formerly wont to emit. The herdsman in charge of the goats marvelled at the strange phenomenon and having approached the chasm and peeped down it to discover what it was, had the same experience as the goats, for the goats began to act like beings possessed and the goatherd also began to foretell future events.

Sources such as these have led generations of scholars to assume that the chasm was the source of the inspiration, and indeed to try and locate it in the archaeological remains of Delphi. There is just one problem: there isn’t one.

The original excavation in 1892 was led by Théophile Homolle, a man who was so disappointed by the missing chasm he is quoted as saying (in Broad 2006):

the temple, on which so much hope had rested, has been a great deception.

And so it seemed, for decades scholars would describe the oracle as a hoax or a scam that misled the pious and the gullible; whether by some intoxicating gas, some unknown drug of some sort, or other hypothesised explanations.

However, geological analysis during the 1980s and 1990s has suggested that two major fault lines cross at Delphi – and under the Temple of Apollo no less. De Boer and Hale (2000) argue that a fissure under the temple, even in the absence of a chasm, could have been enough to allow a small amount of gas to rise up through the rock. Tests of the water that runs beneath the temple and certain rock formation have revealed the presence ethylene, which is known to produce a trance like state when it was formerly used as an anaesthetic. As they conclude, it is certainly possible that this was the source of the Pythia’s inspiration. Whether it came from inhaling the gas, or through ingesting it by drinking the waters, as is suggested by Pausanias among others (10.24.7).

However, there are some problems with this explanation. The first is that this explanation – a chasm that emitted pneuma – is not seen in the source material until the first century BC. Considering that the Delphic Oracle held a central religious importance to the Greek sphere, and appears in great swathes of ancient literature, this late date does appear a little suspect (Scott 2014). Second is the issue of the trance-like, maddened state that Pythia is said to have been in. The Greek words for madness (mania) and divination (mantike) were considered by Plato to be linked (Phaedrus 244 b-c). This allusion seems to appear in the later sources, many of which were written by Christians who aimed to dismiss “pagan” rituals and traditions such as the Oracle.

Yet Plutarch describes an altogether quite different image of the prophetic possessions (Plutarch, Dialogue on Love 16):

After dismounting from the tripod and its spirit, the Pythia continues on into calm and tranquillity.

If the Pythia’s prophecies were brought about during a period of “raving”, that is presumably highly energised and quite distressing periods of activity and speech, then this was short lived.

The origin of the Pythia’s inspiration is not easily identified. It is true that a leading theory includes the possibility of a geological fault that “leaked” gas, which in turn may have affected the Pythia’s mental state, but this theory is not without its problems. Most notably, the behaviours that this explanation covers are not mentioned in the sources before the first century BC.

While the desire to rationalise what we perceive to be irrational is appealing, no concrete answer has yet been offered. For this reason, we have rated the claim as misleading.