Oracle of Delphi

The Pythia (Ancient Greek: Πῡθίᾱ) was the high priestess of the Temple of Apollo at Delphi who served as the god's oracle, more commonly known as the Oracle of Delphi. Established in the 8th century BC, the Pythia was one of the most important and revered of all the ancient oracles, as she was believed to have held a portion of Apollo's actual spirit. The name of the Pythia is derived from the Greek verb πύθειν, which means "to rot" - a reference to the sickly sweet smell which came forth from the rotting corpse of the monstrous serpent Python after she was slain by Apollo. The woman gave up her own name when she became priestess.

While the Pythia was believed to have been possessed by Apollo himself when delivering prophecies, recently, scholars suggested that volcanic gases played their part in her strange utterings.

Croesus of Lydia

In 560 BC Croesus, King of Lydia, selected the Delphic Oracle and the Oracle at Thebes for advice. He asked if he should make war on the Persians. Both oracles gave the same response, that if Croesus made war on the Persians, he would destroy a mighty empire. They also advised him to seek out the most powerful Greek peoples and make alliance with them.

Croesus paid a high fee to the Delphians and then sent to the oracle asking "Would his monarchy last long?" The Pythia answered:

Whenever a mule shall become sovereign king of the Medes, then flee, and think not to stand fast, nor shame to be chicken-hearted.

Croesus thought it impossible that a mule should be king of the Medes and thus believed that he and his issue would never be out of power. He thus decided to make common cause with certain Greek city states and attack Persia.

However, it was he, not the Persians, who was defeated. This fulfilled the prophecy but not his interpretation of it. Apparently, he forgot that Cyrus, the victor, was half Mede (by his mother), half Persian (by his father) and so could be considered a mule.