The name Delphi comes from the same root as δελφύς delphys, "womb" and may indicate archaic veneration of Gaia at the site.
Apollo is connected with the site by his epithet Δελφίνιος Delphinios, "the Delphinian".
The epithet is connected with dolphins (Greek δελφίς,-ῖνος) in the Homeric Hymn to Apollo (line 400), recounting the legend of how Apollo first came to Delphi in the shape of a dolphin, carrying Cretan priests on his back.
The Homeric name of the oracle is Pytho (Πυθώ).
Another legend held that Apollo walked to Delphi from the north and stopped at Tempe, a city in Thessaly, to pick laurel (also known as bay tree) which he considered to be a sacred plant.
In commemoration of this legend, the winners at the Pythian Games received a wreath of laurel picked in the temple.

Delphi became the site of a major temple to Phoebus Apollo, as well as the Pythian Games and the prehistoric oracle.
Even in Roman times, hundreds of votive statues remained, described by Pliny the Younger and seen by Pausanias.
Carved into the temple were three phrases: γνῶθι σεαυτόν (gnōthi seautón = "know thyself") and μηδὲν ἄγαν (mēdén ágan = "nothing in excess"), and Ἑγγύα πάρα δ'ἄτη (engýa pára d'atē = "make a pledge and mischief is nigh"), In antiquity, the origin of these phrases was attributed to one or more of the Seven Sages of Greece by authors such as Plato and Pausanias.
Additionally, according to Plutarch's essay on the meaning of the "E at Delphi"—the only literary source for the inscription—there was also inscribed at the temple a large letter E. Among other things epsilon signifies the number 5.
However, ancient as well as modern scholars have doubted the legitimacy of such inscriptions.
According to one pair of scholars, "The actual authorship of the three maxims set up on the Delphian temple may be left uncertain.
Most likely they were popular proverbs, which tended later to be attributed to particular sages."

According to the Homeric hymn to the Pythian Apollo, Apollo shot his first arrow as an infant which effectively slew the serpent Pytho, the son of Gaia, who guarded the spot.
To atone the murder of Gaia's son, Apollo was forced to fly and spend eight years in menial service before he could return forgiven.
A festival, the Septeria, was held every year, at which the whole story was represented: the slaying of the serpent, and the flight, atonement, and return of the god.

The Pythian Games took place every four years to commemorate Apollo's victory.
Another regular Delphi festival was the "Theophania" (Θεοφάνεια), an annual festival in spring celebrating the return of Apollo from his winter quarters in Hyperborea.
The culmination of the festival was a display of an image of the gods, usually hidden in the sanctuary, to worshippers.

The theoxenia was held each summer, centred on a feast for "gods and ambassadors from other states."
Myths indicate that Apollo killed the chthonic serpent Python guarding the Castalian Spring and named his priestess Pythia after her.
 Python, who had been sent by Hera, had attempted to prevent Leto, while she was pregnant with Apollo and Artemis, from giving birth.

This spring flowed toward the temple but disappeared beneath, creating a cleft which emitted chemical vapors that purportedly caused the oracle at Delphi to reveal her prophecies.
Apollo killed Python but had to be punished for it, since he was a child of Gaia.
The shrine dedicated to Apollo was originally dedicated to Gaia and shared with Poseidon.
The name Pythia remained as the title of the Delphic oracle.

Erwin Rohde wrote that the Python was an earth spirit, who was conquered by Apollo, and buried under the omphalos, and that it is a case of one deity setting up a temple on the grave of another.
Another view holds that Apollo was a fairly recent addition to the Greek pantheon coming originally from Lydia.
The Etruscans coming from northern Anatolia also worshipped Apollo, and it may be that he was originally identical with Mesopotamian Aplu, an Akkadian title meaning "son", originally given to the plague God Nergal, son of Enlil.
The name Delphi comes from the same root as δελφύς delphys, "womb" and may indicate archaic veneration of Gaia at the site. Apollo is connected with the site by his epithet Δελφίνιος Delphinios, "the Delphinian". The epithet is connected with dolphins (Greek δελφίς,-ῖνος) in the Homeric Hymn to Apollo (line 400), recounting the legend of how Apollo first came to Delphi in the shape of a dolphin, carrying Cretan priests on his back. The Homeric name of the oracle is Pytho (Πυθώ). Another legend held that Apollo walked to Delphi from the north and stopped at Tempe, a city in Thessaly, to pick laurel (also known as bay tree) which he considered to be a sacred plant. In commemoration of this legend, the winners at the Pythian Games received a wreath of laurel picked in the temple.
Delphi became the site of a major temple to Phoebus Apollo, as well as the Pythian Games and the prehistoric oracle. Even in Roman times, hundreds of votive statues remained, described by Pliny the Younger and seen by Pausanias. Carved into the temple were three phrases: γνῶθι σεαυτόν (gnōthi seautón = "know thyself") and μηδὲν ἄγαν (mēdén ágan = "nothing in excess"), and Ἑγγύα πάρα δ'ἄτη (engýa pára d'atē = "make a pledge and mischief is nigh"), In antiquity, the origin of these phrases was attributed to one or more of the Seven Sages of Greece by authors such as Plato and Pausanias. Additionally, according to Plutarch's essay on the meaning of the "E at Delphi"—the only literary source for the inscription—there was also inscribed at the temple a large letter E. Among other things epsilon signifies the number 5. However, ancient as well as modern scholars have doubted the legitimacy of such inscriptions. According to one pair of scholars, "The actual authorship of the three maxims set up on the Delphian temple may be left uncertain. Most likely they were popular proverbs, which tended later to be attributed to particular sages."
According to the Homeric hymn to the Pythian Apollo, Apollo shot his first arrow as an infant which effectively slew the serpent Pytho, the son of Gaia, who guarded the spot. To atone the murder of Gaia's son, Apollo was forced to fly and spend eight years in menial service before he could return forgiven. A festival, the Septeria, was held every year, at which the whole story was represented: the slaying of the serpent, and the flight, atonement, and return of the god.
The Pythian Games took place every four years to commemorate Apollo's victory. Another regular Delphi festival was the "Theophania" (Θεοφάνεια), an annual festival in spring celebrating the return of Apollo from his winter quarters in Hyperborea. The culmination of the festival was a display of an image of the gods, usually hidden in the sanctuary, to worshippers.
The theoxenia was held each summer, centred on a feast for "gods and ambassadors from other states." Myths indicate that Apollo killed the chthonic serpent Python guarding the Castalian Spring and named his priestess Pythia after her.  Python, who had been sent by Hera, had attempted to prevent Leto, while she was pregnant with Apollo and Artemis, from giving birth.
This spring flowed toward the temple but disappeared beneath, creating a cleft which emitted chemical vapors that purportedly caused the oracle at Delphi to reveal her prophecies. Apollo killed Python but had to be punished for it, since he was a child of Gaia. The shrine dedicated to Apollo was originally dedicated to Gaia and shared with Poseidon. The name Pythia remained as the title of the Delphic oracle.
Erwin Rohde wrote that the Python was an earth spirit, who was conquered by Apollo, and buried under the omphalos, and that it is a case of one deity setting up a temple on the grave of another. Another view holds that Apollo was a fairly recent addition to the Greek pantheon coming originally from Lydia. The Etruscans coming from northern Anatolia also worshipped Apollo, and it may be that he was originally identical with Mesopotamian Aplu, an Akkadian title meaning "son", originally given to the plague God Nergal, son of Enlil. 
Delphi