Wikipedia:
Delphi... in legend previously called Pytho (Πυθώ), was an ancient sacred precinct and the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient classical world. The ancient Greeks considered the center of the world to be in Delphi, marked by the stone monument known as the Omphalos of Delphi (navel).
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Original position of the Omphalos:
Wikipedia:
It is part of an ancient Greek sacrificial tripod, originally in Delphi and relocated to Constantinople by Constantine the Great in 324. It was built to commemorate the Greeks who fought and defeated the Persian Empire at the Battle of Plataea (479 BC). The serpent heads of the 8-metre (26 ft) high column remained intact until the end of the 17th century (one is on display at the nearby Istanbul Archaeology Museums).