In myths dating to the classical periodof Ancient Greece (510-323 BC), the site of Delphi was believed to be determined by Zeus when he sought to find the centre of his "Grandmother Earth" (Ge, Gaea, or Gaia). He sent two eagles flying from the eastern and western extremities, and the path of the eagles crossed over Delphi where the omphalos, or navel of Gaia was found.
Earlier myths include traditions that Pythia, or the Delphic oracle, already was the site of an important oracle in the pre-classical Greek world (as early as 1400 BC) and, rededicated from about 800 BCE, when it served as the major site during classical times for the worship of the god Apollo. Apollo was said to have slain Python, "a dragon" who lived there and protected the navel of the Earth. "Python" (derived from the verb pythein, "to rot") is claimed by some to be the original name of the site in recognition of Python which Apollo defeated. The Homeric Hymn to Delphic Apollo recalled that the ancient name of this site had been Krisa. Others relate that it was named Pytho and that Pythia, the priestess serving as the oracle, was chosen from their ranks by a group of priestesses who officiated at the temple.
Apollo's sacred precinct in Delphi was a panhellenic sanctuary, where every four years, starting in 586 BC athletes from all over the Greek world competed in the Pythian Games, one of the four panhellenic (or stephanitic) games, precursors of the Modern Olympics. The victors at Delphi were presented with a laurel crown (stephanos) which was ceremonially cut from a tree by a boy who re-enacted the slaying of the Python. Delphi was set apart from the other games sites because it hosted the mousikos agon, musical competitions.
These Pythian Games rank second among the four stephanitic games chronologically and based on importance. These games, though, were different from the games at Olympia in that they were not of such vast importance to the city of Delphi as the games at Olympia were to the area surrounding Olympia. Delphi would have been a renowned city whether or not it hosted these games; it had other attractions that led to it being labeled the "omphalos" (navel) of the earth, in other words, the center of the world.
In the inner hestia ("hearth") of the Temple of Apollo, an eternal flame burned. After the battle of Plataea, the Greek cities extinguished their fires and brought new fire from the hearth of Greece, at Delphi; in the foundation stories of several Greek colonies, the founding colonists were first dedicated at Delphi.
The Delphic Oracle exerted considerable influence throughout the Greek world, and she was consulted before all major undertakings: wars, the founding of colonies, and so forth. She also was respected by the Greek-influenced countries around the periphery of the Greek world, such as Lydia, Caria, and even Egypt. The oracle was also known to the early Romans. Rome's seventh and last king, Lucius Tarquinius Superbus, after witnessing a snake near his palace, sent a delegation including two of his sons to consult the oracle.
The Oracle benefited from the patronage of the Macedonian kings. Later it was placed under the protection of the Aetolian League, which played the leading role in repelling the Gallic invasion of Brennus in 279 BC and saving the sanctuary. Delphi, under the domination of the Aetolians, enjoyed a period of peace until 168-167 BC, when the Romans were eventually able to permanently dominate the region. The Roman Republic protected the Oracle from a dangerous barbarian invasion in 109 BC and 105 BC. In 86 BC, during the Mithridatic Wars, the Roman general Sulla ordered the Amphictyons of Delphi to send him the precious metal offerings of the temple. They obeyed the order without objection, fearing the Roman power. Three years later, Medi, a Thracian tribe, raided Delphi, burned the temple, plundered the sanctuary and stole the “unquenchable fire” from the altar. During the raid, part of the temple roof collapsed. The same year, the Temple was severely damaged by an earthquake. Thus the Oracle fell in decay and the surrounding area became impoverished. The sparse local population led to difficulties in filling the posts required. The Oracle's credibility waned due to doubtful predictions.
When Nero came to Greece in AD 66, he took away over 500 of the best statues from Delphi to Rome. Subsequent Roman emperors of the Flavian dynasty contributed significantly towards its restoration. The oracle relatively flourished again during the rule of emperor Hadrian, who is believed to have visited the oracle twice. Also, Hadrian offered complete autonomy to the city. Plutarch was a significant factor too, by his presence as a chief priest. Barbarian raids commenced again during the reign of Marcus Aurelius.
By the 4th century, Delphi had acquired the status of a city, which was located to the west of the sanctuary grounds. Constantine the Great looted several monuments, most notably the Tripod of Plataea, which he used to decorate his new capital, Constantinople.
Despite the rise of Christianity across the Roman Empire, the oracle remained an active pagan centre throughout the 4th century, and the Pythian Games continued to be held at least until 424; however, the decline continued. The attempt of emperor Julian the Apostate to revive the dying ancient world, and with it the pagan religion, proved unsuccessful. Excavations have revealed a large three-aisled basilica in the city, as well as traces of a church building in the sanctuary's gymnasium. The site was abandoned in the 6th or 7th centuries, although a single bishop of Delphi is attested in an episcopal list of the late 8th/early 9th centuries.
Time and natural disasters added to the picture of desolation of the once glorious place, and the small and insignificant village of Kastri was founded on the site.
Source: wikipedia.org