The Omphalos is a dome-shaped item with light decoration that was in the backside of the Temple of Apollo, and it was used by Pythia for the prophecies. Its usage is not very clear due to the mysteries surrounding the oracle. Omphalos is a Greek word for the navel. This is, of course, a symbolism. Delphi has been described as the center of the world, as the navel is the center of the human body. There is also a very popular myth that supports this idea. According to the myth, Zeus wanted to find out where the center of the world was. As he was eating on top of Mount Olympus, he decided to release two eagles, one towards the east and the other towards the west. The two eagles met exactly at the center, which of course happened to be Delphi. The thinking behind this idea of Delphi being the center of the world is not as bizarre as it may seem. In a way, Delphi was indeed the center of the known world back then in those times. People would travel from many different lands to visit Delphi and receive a prophecy from the oracle. For more information visit Delphi.com.