An omphalos is an ancient religious stone artifact, or baetylus. In Greek, the word omphalos means "navel" (compare the name of Queen Omphale). According to the ancient Greeks, Zeus sent out two eagles to fly across the world to meet at its center, the "navel" of the world. Omphalos stones used to denote this point were erected in several areas surrounding the Mediterranean Sea; the most famous of those was at the oracle in Delphi. The plant genus Omphalodes in the family Boraginaceae is commonly called navelwort.
The Omphalos at Delphi came to be identified as the stone which Rhea wrapped in swaddling clothes, pretending it was Zeus. This was to deceive Cronus, his father, who swallowed his children so they could not grow up and depose him as he had deposed his own father, Uranus.
Omphalos stones were said to allow direct communication with the gods. Leicester Holland (1933) has suggested that the stone was hollow to channel intoxicating vapours breathed by the Oracle. Erwin Rohde wrote that the Python at Delphi was an earth spirit, who was conquered by Apollo, and buried under the Omphalos, and that it is a case of one god setting up his temple on the grave of another.
Billy Pitt had them built, Buck Mulligan said, when the French were on the sea. But ours is the OMPHALOS.In chapter 14, Mulligan proposes:
... to set up there a national fertilising farm to be named OMPHALOS with an obelisk hewn and erected after the fashion of Egypt and to offer his dutiful yeoman services for the fecundation of any female of what grade of life soever who should there direct to him with the desire of fulfilling the functions of her natural.
The first of the Indiana Jones Bantam Books series, Indiana Jones and the Peril at Delphi, features the Omphalos as the MacGuffin. In the novel, the omphalos is described as a small smooth black cone with a knotted net covering its surface. The netting is described as being petrified rather than carved as it is on the real world omphalos at Delphi. When one holds the omphalos they can see into the near and distant future.